Zoom lens system, imaging device and camera

ABSTRACT

A zoom lens system according to the present invention, from an object side to an image side, comprises a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having positive optical power, and a fourth lens unit having positive optical power. In zooming, the first to the fourth lens units all move along the optical axis. The condition (8): 0.15&lt;dG3/dG&lt;0.27 is satisfied (where, 16&lt;f T /f W , ω&gt;35; dG3 is an optical axial center thickness of the third lens unit; dG is a sum of the optical axial thicknesses of the first to the fourth lens units; ω is a half view angle at a wide-angle limit; f T  is a focal length of the entire system at a telephoto limit; and f W  is a focal length of the entire system at a wide-angle limit). As a result, the zoom lens system has a reduced size and still realizes a wide view angle at a wide-angle limit, as well as a remarkably high zooming ratio and high performance.

TECHNICAL FIELD

The present invention relates to a zoom lens system, an imaging deviceand a camera. In particular, the present invention relates to: a zoomlens system having a reduced size and still realizing a wide view angleat a wide-angle limit, as well as a remarkably high zooming ratio andhigh performance; an imaging device employing this zoom lens system; anda thin and compact camera employing this imaging device.

BACKGROUND ART

Remarkably strong demands are present for improved performance ofcameras such as digital still cameras and digital video cameras (simplyreferred to as digital cameras, hereinafter) provided with an imagesensor for performing photoelectric conversion. In particular, in orderthat a single digital camera should be capable of covering a wide focallength range from a wide-angle condition to a high telephoto condition,cameras employing a zoom lens system having a remarkably high zoomingratio are strongly demanded from a convenience point of view. Further,in recent years, zoom lens systems are also desired that have a wideangle range where the photographing field is wide.

As zoom lens systems having high zooming ratios and suitable for theabove-mentioned digital cameras, for example, the following zoom lenssystems have been proposed.

For example, Japanese Laid-Open Patent Publication No. 2006-171655discloses an image-taking optical system at least comprising a firstlens unit having positive optical power, a second lens unit havingnegative optical power, a third lens unit having positive optical power,and a fourth lens unit having positive optical power, wherein any of thelens unit intervals is changed so that variable magnification isachieved, and wherein the ratio between the focal length of the thirdlens unit and the focal length of the fourth lens unit and the ratiobetween the focal length of the first lens unit and the focal length ofthe entire optical system at a wide-angle limit are set forth.

Japanese Laid-Open Patent Publication No. 2006-184413 discloses animage-taking optical system at least comprising a first lens unit havingpositive optical power, a second lens unit having negative opticalpower, a third lens unit having positive optical power, and a fourthlens unit having positive optical power, wherein at least the first lensunit is moved so that variable magnification is achieved, and whereinthe ratio between the distance from the surface located on the mostimage-taking object side in the first lens unit at a wide-angle limit tothe image formation surface and the focal length of the entire opticalsystem at a telephoto limit and the ratio between the focal length ofthe first lens unit and the focal length of the entire optical system ata wide-angle limit are set forth.

Japanese Laid-Open Patent Publication No. 2006-184416 discloses animage-taking optical system at least comprising a first lens unit havingpositive optical power, a second lens unit having negative opticalpower, a third lens unit having positive optical power, and a fourthlens unit having positive optical power, wherein any of the lens unitintervals is changed so that variable magnification is achieved, andwherein the ratio between the focal length of the first lens unit andthe focal length of the entire optical system at a wide-angle limit, theratio between the ratio of the focal length of the second lens unit at atelephoto limit and at a wide-angle limit and the ratio of the focallength of the entire optical system at a telephoto limit and at awide-angle limit, and the ratio between the magnification of the thirdlens unit at a telephoto limit and the magnification of the third lensunit at a wide-angle limit are set forth.

Japanese Laid-Open Patent Publication No. 2006-189598 discloses animage-taking optical system at least comprising a first lens unit havingpositive optical power, a second lens unit having negative opticalpower, a third lens unit having positive optical power, and a fourthlens unit having positive optical power, wherein the third lens unit atleast includes two positive optical power lenses and one negativeoptical power lens, wherein at least the second, the third, and thefourth lens units are moved so that variable magnification is achieved,and wherein the ratio between the focal length of the first lens unitand the focal length of the entire optical system at a wide-angle limit,the ratio between the focal length of the negative optical power lens inthe third lens unit and the focal length of the third lens unit, and therefractive index of the negative optical power lens in the third lensunit are set forth.

Japanese Laid-Open Patent Publication No. 2007-003554 discloses avariable magnification optical system at least comprising a first lensunit having positive optical power, a second lens unit having negativeoptical power, a third lens unit having positive optical power, and afourth lens unit having positive optical power, wherein at least thefirst and the third lens units are moved so that variable magnificationis achieved, wherein in this magnification change, the first lens unitis moved to the object side, and wherein the ratio between the amount ofrelative movement of the second lens unit at the time of magnificationchange and the focal length of the entire optical system at a wide-anglelimit, the ratio between the focal length of the first lens unit and thefocal length of the entire optical system at a wide-angle limit, and theratio between the focal length of the third lens unit and the focallength of the entire optical system at a telephoto limit are set forth.

Japanese Laid-Open Patent Publication No. 2007-010695 discloses avariable magnification optical system at least comprising a first lensunit having positive optical power, a second lens unit having negativeoptical power, a third lens unit having positive optical power, and afourth lens unit having positive optical power, wherein at least thefirst lens unit is moved so that variable magnification is achieved, andwherein the ratio between the focal length of the first lens unit andthe focal length of the entire optical system at a wide-angle limit andthe average refractive index to the d-line of all lenses in the secondlens unit are set forth.

Patent Document 1: Japanese Laid-Open Patent Publication No. 2006-171655Patent Document 2: Japanese Laid-Open Patent Publication No. 2006-184413Patent Document 3: Japanese Laid-Open Patent Publication No. 2006-184416Patent Document 4: Japanese Laid-Open Patent Publication No. 2006-189598Patent Document 5: Japanese Laid-Open Patent Publication No. 2007-003554Patent Document 6: Japanese Laid-Open Patent Publication No. 2007-010695DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The optical systems disclosed in the above-mentioned publications havehigh zooming ratios sufficient for application to digital cameras.Nevertheless, width of the view angle at a wide-angle limit and sizereduction are not simultaneously realized. In particular, from theviewpoint of size reduction, requirements in digital cameras of recentyears are not satisfied.

Objects of the present invention are to provide: a zoom lens systemhaving a reduced size and still realizing a wide view angle at awide-angle limit, as well as a remarkably high zooming ratio and highperformance; an imaging device employing this zoom lens system; and athin and compact camera employing this imaging device.

Solution to the Problems

(I) One of the above-mentioned objects is achieved by the following zoomlens system. That is, the present invention relates to

a zoom lens system, in order from an object side to an image side,comprising a first lens unit having positive optical power, a secondlens unit having negative optical power, a third lens unit havingpositive optical power, and a fourth lens unit having positive opticalpower, wherein

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein

the following condition (8) is satisfied:

0.15<dG3/dG<0.27  (8)

(here, 16<f_(T)/f_(W) and ω>35)

where,

dG3 is an optical axial center thickness of the third lens unit,

dG is a sum of the optical axial thicknesses of the first lens unit, thesecond lens unit, the third lens unit and the fourth lens unit,

ω is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

One of the above-mentioned objects is achieved by the following imagingdevice. That is, the present invention relates to

an imaging device capable of outputting an optical image of an object asan electric image signal, comprising:

a zoom lens system that forms the optical image of the object; and

an image sensor that converts the optical image formed by the zoom lenssystem into the electric image signal, wherein

in the zoom lens system,

the zoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein

the following condition (8) is satisfied:

0.15<dG3/dG<0.27  (8)

(here, 16<f_(T)/f_(W) and ω>35)

where,

dG3 is an optical axial center thickness of the third lens unit,

dG is a sum of the optical axial thicknesses of the first lens unit, thesecond lens unit, the third lens unit and the fourth lens unit,

ω is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

One of the above-mentioned objects is achieved by the following camera.That is, the present invention relates to

a camera for converting an optical image of an object into an electricimage signal and then performing at least one of displaying and storingof the converted image signal, comprising

an imaging device including a zoom lens system that forms the opticalimage of the object and an image sensor that converts the optical imageformed by the zoom lens system into the electric image signal, wherein

in the zoom lens system,

the zoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein

the following condition (8) is satisfied:

0.15<dG3/dG<0.27  (8)

(here, 16<f_(T)/f_(W) and ω>35)

where,

dG3 is an optical axial center thickness of the third lens unit,

dG is a sum of the optical axial thicknesses of the first lens unit, thesecond lens unit, the third lens unit and the fourth lens unit,

ω is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

(II) One of the above-mentioned objects is achieved by the followingzoom lens system. That is, the present invention relates to

a zoom lens system, in order from an object side to an image side,comprising a first lens unit having positive optical power, a secondlens unit having negative optical power, a third lens unit havingpositive optical power, and a fourth lens unit having positive opticalpower, wherein

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein

the following condition (9) is satisfied:

2.7<√/(f ₃ ² +f ₄ ²)/|f ₂|<3.6  (9)

(here, 16<f_(T)/f_(W) and ω>35)

where,

f₂ is a focal length of the second lens unit,

f₃ is a focal length of the third lens unit,

f₄ is a focal length of the fourth lens unit,

ω is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

One of the above-mentioned objects is achieved by the following imagingdevice. That is, the present invention relates to

an imaging device capable of outputting an optical image of an object asan electric image signal, comprising:

a zoom lens system that forms the optical image of the object; and

an image sensor that converts the optical image formed by the zoom lenssystem into the electric image signal, wherein

in the zoom lens system,

the zoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein

the following condition (9) is satisfied:

2.7<√(f ₃ ² +f ₄ ²)/|f ₂|<3.6  (9)

(here, 16<f_(T)/f_(w) and ω>35)

where,

f₂ is a focal length of the second lens unit,

f₃ is a focal length of the third lens unit,

f₄ is a focal length of the fourth lens unit,

ω is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

One of the above-mentioned objects is achieved by the following camera.That is, the present invention relates to

a camera for converting an optical image of an object into an electricimage signal and then performing at least one of displaying and storingof the converted image signal, comprising

an imaging device including a zoom lens system that forms the opticalimage of the object and an image sensor that converts the optical imageformed by the zoom lens system into the electric image signal, wherein

in the zoom lens system,

the zoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein

the following condition (9) is satisfied:

2.7<√(f ₃ ² +f ₄ ²)/|f ₂|<3.6  (9)

(here, 16<f_(T)/f_(W) and ω>35)

where,

f₂ is a focal length of the second lens unit,

f₃ is a focal length of the third lens unit,

f₄ is a focal length of the fourth lens unit,

ω is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

(III) One of the above-mentioned objects is achieved by the followingzoom lens system. That is, the present invention relates to

a zoom lens system, in order from an object side to an image side,comprising a first lens unit having positive optical power, a secondlens unit having negative optical power, a third lens unit havingpositive optical power, and a fourth lens unit having positive opticalpower, wherein

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein

the following condition (III-11) is satisfied:

0.036<d1NG/d1G<0.140  (III-11)

(here, 16<f_(T)/f_(W) and ω>35)

where,

d1NG is an optical axial center thickness of the lens element havingnegative optical power contained in the first lens unit,

d1G is an optical axial center thickness of the first lens unit,

ω is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

One of the above-mentioned objects is achieved by the following imagingdevice. That is, the present invention relates to

an imaging device capable of outputting an optical image of an object asan electric image signal, comprising:

a zoom lens system that forms the optical image of the object; and

an image sensor that converts the optical image formed by the zoom lenssystem into the electric image signal, wherein

in the zoom lens system,

the zoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein

the following condition (III-11) is satisfied:

0.036<d1NG/d1G<0.140  (III-11)

(here, 16<f_(T)/f_(W) and ω>35)

where,

d1NG is an optical axial center thickness of the lens element havingnegative optical power contained in the first lens unit,

d1G is an optical axial center thickness of the first lens unit,

ω is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

One of the above-mentioned objects is achieved by the following camera.That is, the present invention relates to

a camera for converting an optical image of an object into an electricimage signal and then performing at least one of displaying and storingof the converted image signal, comprising

an imaging device including a zoom lens system that forms the opticalimage of the object and an image sensor that converts the optical imageformed by the zoom lens system into the electric image signal, wherein

in the zoom lens system,

the zoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein

in zooming from a wide-angle limit to a telephoto limit, all of thefirst lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein

the following condition (III-11) is satisfied:

0.036<d1NG/d1G<0.140  (III-11)

(here, 16<f_(T)/f_(W) and ω>35)

where,

d1NG is an optical axial center thickness of the lens element havingnegative optical power contained in the first lens unit,

d1G is an optical axial center thickness of the first lens unit,

ω is a half view angle (°) at a wide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

EFFECTS OF THE INVENTION

The present invention provides a zoom lens system having a reduced sizeand still realizes a wide view angle at a wide-angle limit, as well as aremarkably high zooming ratio and high performance. Further, accordingto the present invention, an imaging device employing this zoom lenssystem and a thin and compact camera employing this imaging device areprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiments I-1 and II-1(Examples I-1 and II-1).

FIG. 2 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Examples I-1 and II-1.

FIG. 3 is a lateral aberration diagram in a basic state where image blurcompensation is not performed and in an image blur compensation state ata telephoto limit of a zoom lens system according to Examples I-1 andII-1.

FIG. 4 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiments I-2 and II-2(Examples I-2 and II-2).

FIG. 5 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Examples I-2 and II-2.

FIG. 6 is a lateral aberration diagram in a basic state where image blurcompensation is not performed and in an image blur compensation state ata telephoto limit of a zoom lens system according to Examples I-2 andII-2.

FIG. 7 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiments I-3 and II-3(Examples I-3 and II-3).

FIG. 8 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Examples I-3 and II-3.

FIG. 9 is a lateral aberration diagram in a basic state where image blurcompensation is not performed and in an image blur compensation state ata telephoto limit of a zoom lens system according to Examples I-3 andII-3.

FIG. 10 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiments I-4 and II-4(Examples I-4 and II-4).

FIG. 11 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Examples I-4 and II-4.

FIG. 12 is a lateral aberration diagram in a basic state where imageblur compensation is not performed and in an image blur compensationstate at a telephoto limit of a zoom lens system according to ExamplesI-4 and II-4.

FIG. 13 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiments I-5 and II-5(Examples I-5 and II-5).

FIG. 14 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Examples I-5 and II-5.

FIG. 15 is a lateral aberration diagram in a basic state where imageblur compensation is not performed and in an image blur compensationstate at a telephoto limit of a zoom lens system according to ExamplesI-5 and II-5.

FIG. 16 is a schematic construction diagram of a digital still cameraaccording to Embodiments I-6 and II-6.

FIG. 17 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment III-1 (ExampleIII-1).

FIG. 18 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example III-1.

FIG. 19 is a lateral aberration diagram in a basic state where imageblur compensation is not performed and in an image blur compensationstate at a telephoto limit of a zoom lens system according to ExampleIII-1.

FIG. 20 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment III-2 (ExampleIII-2).

FIG. 21 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example III-2.

FIG. 22 is a lateral aberration diagram in a basic state where imageblur compensation is not performed and in an image blur compensationstate at a telephoto limit of a zoom lens system according to ExampleIII-2.

FIG. 23 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment III-3 (ExampleIII-3).

FIG. 24 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example III-3.

FIG. 25 is a lateral aberration diagram in a basic state where imageblur compensation is not performed and in an image blur compensationstate at a telephoto limit of a zoom lens system according to ExampleIII-3.

FIG. 26 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment III-4 (ExampleIII-4).

FIG. 27 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example III-4.

FIG. 28 is a lateral aberration diagram in a basic state where imageblur compensation is not performed and in an image blur compensationstate at a telephoto limit of a zoom lens system according to ExampleIII-4.

FIG. 29 is a schematic construction diagram of a digital still cameraaccording to Embodiment III-5.

DESCRIPTION OF THE REFERENCE CHARACTERS

-   -   G1 first lens unit    -   G2 second lens unit    -   G3 third lens unit    -   G4 fourth lens unit    -   L1 first lens element    -   L2 second lens element    -   L3 third lens element    -   L4 fourth lens element    -   L5 fifth lens element    -   L6 sixth lens element    -   L7 seventh lens element    -   L8 eighth lens element    -   L9 ninth lens element    -   L10 tenth lens element    -   L11 eleventh lens element    -   L12 twelfth lens element    -   L12, L13 plane parallel plate    -   A diaphragm    -   S image surface    -   1 zoom lens system    -   2 image sensor    -   3 liquid crystal display monitor    -   4 body    -   5 main barrel    -   6 moving barrel    -   7 cylindrical cam

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments I-1 to I-5 and II-1to II-5

FIG. 1 is a lens arrangement diagram of a zoom lens system according toEmbodiments I-1 and II-1. FIG. 4 is a lens arrangement diagram of a zoomlens system according to Embodiments I-2 and II-2. FIG. 7 is a lensarrangement diagram of a zoom lens system according to Embodiments I-3and II-3. FIG. 10 is a lens arrangement diagram of a zoom lens systemaccording to Embodiments I-4 and II-4. FIG. 13 is a lens arrangementdiagram of a zoom lens system according to Embodiments I-5 and II-5.

FIGS. 1, 4, 7, 10 and 13 show respectively a zoom lens system in aninfinity in-focus condition. In each figure, part (a) shows a lensconfiguration at a wide-angle limit (in the minimum focal lengthcondition: focal length f_(W)), part (b) shows a lens configuration at amiddle position (in an intermediate focal length condition: focal lengthf_(M)=√(f_(W)*f_(T))), and part (c) shows a lens configuration at atelephoto limit (in the maximum focal length condition: focal lengthf_(T)). Further, in each figure, bent arrows provided between part (a)and part (b) are lines obtained by connecting the positions of the lensunits at a wide-angle limit, at a middle position and at a telephotolimit, in order from the top to the bottom. Thus, straight lines areused simply between a wide-angle limit and a middle position and betweena middle position and a telephoto limit. That is, these straight linesdo not indicate the actual motion of the individual lens units.Moreover, in each figure, an arrow provided to a lens unit indicatesfocusing from an infinity in-focus condition to a close-object in-focuscondition, that is, the moving direction at the time of focusing from aninfinity in-focus condition to a close-object in-focus condition.

The zoom lens system according to each embodiment, in order from theobject side to the image side, comprises a first lens unit G1 havingpositive optical power, a second lens unit G2 having negative opticalpower, a third lens unit G3 having positive optical power, and a fourthlens unit G4 having positive optical power. Then, in zooming from awide-angle limit to a telephoto limit, the first lens unit G1, thesecond lens unit G2, the third lens unit G3 and the fourth lens unit G4all move along the optical axis (this lens configuration is referred toas the basic configuration I of Embodiments I-1 to I-5 or the basicconfiguration II of Embodiments II-1 to II-5, hereinafter). In the zoomlens system according to each embodiment, these lens units are arrangedinto a desired optical power arrangement, so that a remarkably highzooming ratio exceeding 16 and high optical performance are achieved andstill size reduction is realized in the entire lens system.

In FIGS. 1, 4, 7, 10 and 13, an asterisk “*” provided to a particularsurface indicates that the surface is aspheric. Further, in each figure,a symbol (+) or (−) provided to the sign of each lens unit correspondsto the sign of optical power of the lens unit. Moreover, in each figure,the straight line located on the most right-hand side indicates theposition of an image surface S. On the object side relative to the imagesurface S (between the image surface S and the most image side lenssurface of the fourth lens unit G4), a plane parallel plate such as anoptical low-pass filter and a face plate of an image sensor is provided.Moreover, in each figure, a diaphragm A is provided between the mostimage side lens surface of the second lens unit G2 and the most objectside lens surface of the third lens unit G3.

As shown in FIG. 1, in the zoom lens system according to Embodiments I-1and II-1, the first lens unit G1, in order from the object side to theimage side, comprises: a negative meniscus first lens element L1 withthe convex surface facing the object side; a bi-convex second lenselement L2; and a positive meniscus third lens element L3 with theconvex surface facing the object side. Among these, the first lenselement L1 and the second lens element L2 are cemented with each other.

In the zoom lens system according to Embodiments I-1 and II-1, thesecond lens unit G2, in order from the object side to the image side,comprises: a negative meniscus fourth lens element L4 with the convexsurface facing the object side; a bi-concave fifth lens element L5; abi-convex sixth lens element L6; and a bi-concave seventh lens elementL7. Among these, the sixth lens element L6 and the seventh lens elementL7 are cemented with each other.

Further, in the zoom lens system according to Embodiments I-1 and II-1,the third lens unit G3, in order from the object side to the image side,comprises: a positive meniscus eighth lens element L8 with the convexsurface facing the object side; a bi-convex ninth lens element L9; and abi-concave tenth lens element L10. Among these, the ninth lens elementL9 and the tenth lens element L10 are cemented with each other.

Further, in the zoom lens system according to Embodiments I-1 and II-1,the fourth lens unit G4, in order from the object side to the imageside, comprises: a bi-convex eleventh lens element L11; and a negativemeniscus twelfth lens element L12 with the convex surface facing theimage side. The eleventh lens element L11 and the twelfth lens elementL12 are cemented with each other.

Here, in the zoom lens system according to Embodiments I-1 and II-1, aplane parallel plate L13 is provided on the object side relative to theimage surface S (between the image surface S and the twelfth lenselement L12).

In the zoom lens system according to Embodiments I-1 and II-1, inzooming from a wide-angle limit to a telephoto limit, the first lensunit G1 and the third lens unit G3 move to the object side, while thesecond lens unit G2 moves to the image side, that is, such that theposition at a wide-angle limit should be located on the object siderelative to the position at a telephoto limit. Further, the fourth lensunit G4 moves with locus of a convex to the object side with changingthe interval with the third lens unit G3.

As shown in FIG. 4, in the zoom lens system according to Embodiments I-2and II-2, the first lens unit G1, in order from the object side to theimage side, comprises: a negative meniscus first lens element L1 withthe convex surface facing the object side; a bi-convex second lenselement L2; and a positive meniscus third lens element L3 with theconvex surface facing the object side. Among these, the first lenselement L1 and the second lens element L2 are cemented with each other.

In the zoom lens system according to Embodiments I-2 and II-2, thesecond lens unit G2, in order from the object side to the image side,comprises: a negative meniscus fourth lens element L4 with the convexsurface facing the object side; a bi-concave fifth lens element L5; abi-convex sixth lens element L6; and a bi-concave seventh lens elementL7. Among these, the sixth lens element L6 and the seventh lens elementL7 are cemented with each other.

Further, in the zoom lens system according to Embodiments I-2 and II-2,the third lens unit G3, in order from the object side to the image side,comprises: a positive meniscus eighth lens element L8 with the convexsurface facing the object side; a bi-convex ninth lens element L9; and abi-concave tenth lens element L10. Among these, the ninth lens elementL9 and the tenth lens element L10 are cemented with each other.

Further, in the zoom lens system according to Embodiments I-2 and II-2,the fourth lens unit G4, in order from the object side to the imageside, comprises: a bi-convex eleventh lens element L11; and a negativemeniscus twelfth lens element L12 with the convex surface facing theimage side. The eleventh lens element L11 and the twelfth lens elementL12 are cemented with each other.

Here, in the zoom lens system according to Embodiments I-2 and II-2, aplane parallel plate L13 is provided on the object side relative to theimage surface S (between the image surface S and the twelfth lenselement L12).

In the zoom lens system according to Embodiments I-2 and II-2, inzooming from a wide-angle limit to a telephoto limit, the first lensunit G1 and the third lens unit G3 move to the object side, while thesecond lens unit G2 moves to the image side, that is, such that theposition at a wide-angle limit should be located on the object siderelative to the position at a telephoto limit. Further, the fourth lensunit G4 moves with locus of a convex to the object side with changingthe interval with the third lens unit G3.

As shown in FIG. 7, in the zoom lens system according to Embodiments I-3and II-3, the first lens unit G1, in order from the object side to theimage side, comprises: a negative meniscus first lens element L1 withthe convex surface facing the object side; a positive meniscus secondlens element L2 with the convex surface facing the object side; and apositive meniscus third lens element L3 with the convex surface facingthe object side. Among these, the first lens element L1 and the secondlens element L2 are cemented with each other.

In the zoom lens system according to Embodiments I-3 and II-3, thesecond lens unit G2, in order from the object side to the image side,comprises: a negative meniscus fourth lens element L4 with the convexsurface facing the object side; a bi-concave fifth lens element L5; abi-convex sixth lens element L6; and a bi-concave seventh lens elementL7. Among these, the sixth lens element L6 and the seventh lens elementL7 are cemented with each other.

Further, in the zoom lens system according to Embodiments I-3 and II-3,the third lens unit G3, in order from the object side to the image side,comprises: a positive meniscus eighth lens element L8 with the convexsurface facing the object side; a bi-convex ninth lens element L9; and abi-concave tenth lens element L10. Among these, the ninth lens elementL9 and the tenth lens element L10 are cemented with each other.

Further, in the zoom lens system according to Embodiments I-3 and II-3,the fourth lens unit G4, in order from the object side to the imageside, comprises: a bi-convex eleventh lens element L11; and a negativemeniscus twelfth lens element L12 with the convex surface facing theimage side. The eleventh lens element L11 and the twelfth lens elementL12 are cemented with each other.

Here, in the zoom lens system according to Embodiments I-3 and II-3, aplane parallel plate L13 is provided on the object side relative to theimage surface S (between the image surface S and the twelfth lenselement L12).

In the zoom lens system according to Embodiments I-3 and II-3, inzooming from a wide-angle limit to a telephoto limit, the first lensunit G1 and the third lens unit G3 move to the object side, while thesecond lens unit G2 moves to the image side, that is, such that theposition at a wide-angle limit should be located on the object siderelative to the position at a telephoto limit. Further, the fourth lensunit G4 moves with locus of a convex to the object side with changingthe interval with the third lens unit G3.

As shown in FIG. 10, in the zoom lens system according to EmbodimentsI-4 and II-4, the first lens unit G1, in order from the object side tothe image side, comprises: a negative meniscus first lens element L1with the convex surface facing the object side; a positive meniscussecond lens element L2 with the convex surface facing the object side;and a positive meniscus third lens element L3 with the convex surfacefacing the object side. Among these, the first lens element L1 and thesecond lens element L2 are cemented with each other.

In the zoom lens system according to Embodiments I-4 and II-4, thesecond lens unit G2, in order from the object side to the image side,comprises: a negative meniscus fourth lens element L4 with the convexsurface facing the object side; a bi-concave fifth lens element L5; anda positive meniscus sixth lens element L6 with the convex surface facingthe object side.

Further, in the zoom lens system according to Embodiments I-4 and II-4,the third lens unit G3, in order from the object side to the image side,comprises: a positive meniscus seventh lens element L7 with the convexsurface facing the object side; a bi-convex eighth lens element L8; anda bi-concave ninth lens element L9. Among these, the eighth lens elementL8 and the ninth lens element L9 are cemented with each other.

Further, in the zoom lens system according to Embodiments I-4 and II-4,the fourth lens unit G4, in order from the object side to the imageside, comprises: a bi-convex tenth lens element L10; and a negativemeniscus eleventh lens element L11 with the convex surface facing theimage side. The tenth lens element L10 and the eleventh lens element L11are cemented with each other.

Here, in the zoom lens system according to Embodiments I-4 and II-4, aplane parallel plate L12 is provided on the object side relative to theimage surface S (between the image surface S and the eleventh lenselement L11).

In the zoom lens system according to Embodiments I-4 and II-4, inzooming from a wide-angle limit to a telephoto limit, the first lensunit G1 and the third lens unit G3 move to the object side, while thesecond lens unit G2 moves to the image side, that is, such that theposition at a wide-angle limit should be located on the object siderelative to the position at a telephoto limit. Further, the fourth lensunit G4 moves with locus of a convex to the object side with changingthe interval with the third lens unit G3.

As shown in FIG. 13, in the zoom lens system according to EmbodimentsI-5 and II-5, the first lens unit G1, in order from the object side tothe image side, comprises: a negative meniscus first lens element L1with the convex surface facing the object side; a bi-convex second lenselement L2; and a positive meniscus third lens element L3 with theconvex surface facing the object side. Among these, the first lenselement L1 and the second lens element L2 are cemented with each other.

In the zoom lens system according to Embodiments I-5 and II-5, thesecond lens unit G2, in order from the object side to the image side,comprises: a negative meniscus fourth lens element L4 with the convexsurface facing the object side; a bi-concave fifth lens element L5; anda positive meniscus sixth lens element L6 with the convex surface facingthe object side.

Further, in the zoom lens system according to Embodiments I-5 and II-5,the third lens unit G3, in order from the object side to the image side,comprises: a positive meniscus seventh lens element L7 with the convexsurface facing the object side; a bi-convex eighth lens element L8; anda bi-concave ninth lens element L9. Among these, the eighth lens elementL8 and the ninth lens element L9 are cemented with each other.

Further, in the zoom lens system according to Embodiments I-5 and II-5,the fourth lens unit G4, in order from the object side to the imageside, comprises: a bi-convex tenth lens element L10; and a negativemeniscus eleventh lens element L11 with the convex surface facing theimage side. The tenth lens element L10 and the eleventh lens element L11are cemented with each other.

Here, in the zoom lens system according to Embodiments I-5 and II-5, aplane parallel plate L12 is provided on the object side relative to theimage surface S (between the image surface S and the eleventh lenselement L11).

In the zoom lens system according to Embodiments I-5 and II-5, inzooming from a wide-angle limit to a telephoto limit, the first lensunit G1 and the third lens unit G3 move to the object side, while thesecond lens unit G2 moves to the image side, that is, such that theposition at a wide-angle limit should be located on the object siderelative to the position at a telephoto limit. Further, the fourth lensunit G4 moves with locus of a convex to the object side with changingthe interval with the third lens unit G3.

In the zoom lens system according to each embodiment, in zooming from awide-angle limit to a telephoto limit, the first lens unit G1, thesecond lens unit G2, the third lens unit G3 and the fourth lens unit G4all move along the optical axis. Among these lens units, for example,the third lens unit is moved in a direction perpendicular to the opticalaxis, so that image blur caused by hand blurring, vibration and the likecan be compensated optically.

In the present invention, when the image blur is to be compensatedoptically, the third lens unit moves in a direction perpendicular to theoptical axis as described above, so that image blur is compensated in astate that size increase in the entire zoom lens system is suppressedand a compact construction is realized and that excellent imagingcharacteristics such as small decentering coma aberration anddecentering astigmatism are satisfied.

The following description is given for conditions desired to besatisfied by a zoom lens system having the above-mentioned basicconfiguration I like the zoom lens system according to Embodiments I-1to I-5 or a zoom lens system having the above-mentioned basicconfiguration II like the zoom lens system according to Embodiments II-1to II-5. Here, a plurality of preferable conditions are set forth forthe zoom lens system according to each embodiment. A construction thatsatisfies all the plural conditions is most desirable for the zoom lenssystem. However, when an individual condition is satisfied, a zoom lenssystem having the corresponding effect can be obtained.

Further, all conditions described below hold only under the followingtwo premise conditions, unless noticed otherwise.

16<f _(T) /f _(W)

w>35

where,

f_(T) is a focal length of the entire system at a telephoto limit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

ω is a half view angle (°) at a wide-angle limit.

The zoom lens system having the basic configuration I satisfies thefollowing condition (8).

0.15<dG3/dG<0.27  (8)

where,

dG3 is an optical axial center thickness of the third lens unit, and

dG is a sum of the optical axial thicknesses of the first lens unit, thesecond lens unit, the third lens unit and the fourth lens unit.

The condition (8) sets forth the optical axial thickness of the thirdlens unit. When the value exceeds the upper limit of the condition (8),the thickness of the third lens unit is excessively great and hence acompact lens system is not realized. Further, when the value exceeds theupper limit of the condition (8), the thickness of the third lens unitis excessively great, and hence it becomes difficult that the third lensunit is moved in a direction perpendicular to the optical axis for blurcompensation. In contrast, when the value goes below the lower limit ofthe condition (8), various kinds of aberration to be compensated by thethird lens unit, especially, spherical aberration and coma aberration ata wide-angle limit cannot be compensated.

Here, when at least one of the following conditions (8)′ and (8)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.19<dG3/dG  (8)′

dG3/dG<0.22  (8)′

The zoom lens system having the basic configuration II satisfies thefollowing condition (9).

2.7<√(f ₃ ² +f ₄ ²)/|f ₂|<3.6  (9)

where,

f₂ is a focal length of the second lens unit,

f₃ is a focal length of the third lens unit, and

f₄ is a focal length of the fourth lens unit.

The condition (9) sets forth the focal lengths of the lens units. Whenthe value exceeds the upper limit of the condition (9), the absolutevalue of the optical power of the second lens unit is relatively strongexcessively. Thus, various kinds of aberration, especially, distortionat a wide-angle limit cannot be compensated. In contrast, when the valuegoes below the lower limit of the condition (9), the absolute value ofthe optical power of the second lens unit is relatively weakexcessively. Thus, in a case that a zoom lens system having a highmagnification is to be achieved, the necessary amount of movement of thesecond lens unit is excessively great.

Here, when at least one of the following conditions (9)′ and (9)″ issatisfied, the above-mentioned effect is achieved more successfully.

2.8<√/(f ₃ ² +f ₄ ²)/|f ₂|  (9)′

√(f ₃ ² +f ₄ ²)/|f ₂|<3.5  (9)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (1) is satisfied.

0<√(f ₄ ·f _(w)·tan ω)/L _(W)<0.13  (1)

where,

ω is a half view angle (°) at a wide-angle limit,

L_(W) is an overall optical axial length of the entire system at awide-angle limit (a distance from the most object side surface to themost image side surface),

f₄ is a focal length of the fourth lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (1) substantially sets forth the focal length of thefourth lens unit. When the value exceeds the upper limit of thecondition (1), the optical power of the fourth lens unit is excessivelyweak, and hence the necessary amount of movement in zooming increases.Thus, it is difficult in some cases to achieve a thin lens barrelconfiguration. Further, when the value exceeds the upper limit of thecondition (1), it becomes difficult to achieve a satisfactory peripheralilluminance on the image surface especially at a wide-angle limit. Thus,this situation is not preferable.

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (2) is satisfied.

0.05≦f ₃ /f ₄≦0.97  (2)

where,

f₃ is a focal length of the third lens unit, and

f₄ is a focal length of the fourth lens unit.

The condition (2) sets forth the ratio between the focal length of thethird lens unit and the focal length of the fourth lens unit. When thevalue exceeds the upper limit of the condition (2), the focal length ofthe third lens unit is excessively long. Thus, a possibility arises thatthe amount of movement of the third lens unit necessary for achieving ahigh magnification exceeding 16 increases excessively. Further, when thevalue exceeds the upper limit of the condition (2), in some cases, itbecomes difficult that, for example, the third lens unit is moved in adirection perpendicular to the optical axis for blur compensation. Incontrast, when the value goes below the lower limit of the condition(2), the focal length of the third lens unit is excessively short. Thus,a large aberration fluctuation arises in zooming so as to causedifficulty in compensation. Further, the absolute values of variouskinds of aberration generated in the third lens unit increaseexcessively, and hence compensation becomes difficult. Thus, thissituation is not preferable. Moreover, when the value goes below thelower limit of the condition (2), an excessively high error sensitivityto the inclination between the surfaces in the third lens unit iscaused. This causes in some cases difficulty in assembling the opticalsystem.

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, especially in acase that the second lens unit includes a lens element having negativeoptical power and being arranged on the most object side and a lenselement having positive optical power, it is preferable that thefollowing condition (3) is satisfied.

(nd ₄−1)+(nd ₆−1)≧1.8  (3)

where,

nd₄ is a refractive index to the d-line of a lens element havingnegative optical power and being arranged on the most object side in thesecond lens unit, and

nd₆ is a refractive index to the d-line of a lens element havingpositive optical power in the second lens unit.

The condition (3) sets forth a condition desired to be satisfied by lenselements contained in the second lens unit. When the value falls outsidethe range of the condition (3), compensation of distortion and curvatureof field is difficult especially at a wide-angle limit. Thus, thissituation is not preferable.

Here, when the following condition (3)′ is satisfied, theabove-mentioned effect is achieved more successfully.

(nd ₄−1)+(nd ₆−1)≧1.9  (3)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, especially in acase that the first lens unit includes a lens element having negativeoptical power and being arranged on the most object side and a lenselement having positive optical power, it is preferable that thefollowing condition (4) is satisfied.

nd ₁ −nd ₂0.5  (4)

where,

nd₁ is a refractive index to the d-line of a lens element havingnegative optical power and being arranged on the most object side in thefirst lens unit, and

nd₂ is a refractive index to the d-line of a lens element located on themost object side among the lens elements having positive optical powerin the first lens unit.

The condition (4) sets forth a condition desired to be satisfied by lenselements contained in the first lens unit. When the value falls outsidethe range of the condition (4), compensation of chromatic aberration,especially, axial chromatic aberration, at a telephoto limit isdifficult. Thus, this situation is not preferable.

Here, when the following condition (4)′ is satisfied, theabove-mentioned effect is achieved more successfully.

nd ₁ −nd ₂≧0.6  (4)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, especially in acase that the first lens unit includes a lens element having negativeoptical power and being arranged on the most object side and a lenselement having positive optical power and being arranged on the mostimage side, it is preferable that the following condition (5) issatisfied.

(nd ₁−1)+(nd ₃−1)≧1.8  (5)

where,

nd₁ is a refractive index to the d-line of a lens element havingnegative optical power and being arranged on the most object side in thefirst lens unit, and

nd₃ is a refractive index to the d-line of a lens element havingpositive optical power and being arranged on the most image side in thefirst lens unit.

The condition (5) sets forth a condition desired to be satisfied by lenselements contained in the first lens unit. When the value falls outsidethe range of the condition (5), compensation of chromatic aberration,especially, axial chromatic aberration, at a telephoto limit isdifficult. Thus, this situation is not preferable.

Here, when the following condition (5)′ is satisfied, theabove-mentioned effect is achieved more successfully.

(nd ₁−1)+(nd ₃−1)≧1.9  (5)′

In a zoom lens system having the above-mentioned basic configuration IIlike each zoom lens system according to Embodiments II-1 to II-5, it ispreferable that the following condition (8) is satisfied.

0.15<dG3/dG<0.27  (8)

where,

dG3 is an optical axial center thickness of the third lens unit, and

dG is a sum of the optical axial thicknesses of the first lens unit, thesecond lens unit, the third lens unit and the fourth lens unit.

The condition (8) sets forth the optical axial thickness of the thirdlens unit. When the value exceeds the upper limit of the condition (8),the thickness of the third lens unit is excessively great, and hence itis difficult in some cases to achieve a compact lens system. Further,when the value exceeds the upper limit of the condition (8), thethickness of the third lens unit is excessively great, and hence itbecomes difficult that, for example, the third lens unit is moved in adirection perpendicular to the optical axis for blur compensation. Incontrast, when the value goes below the lower limit of the condition(8), difficulty arises in compensating various kinds of aberration to becompensated by the third lens unit, especially in compensating sphericalaberration and coma aberration at a wide-angle limit. Thus, thissituation is not preferable.

Here, when at least one of the following conditions (8)′ and (8)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.19<dG3/dG  (8)′

dG3/dG<0.22  (8)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5, it ispreferable that the following condition (9) is satisfied.

2.7<√(f ₃ ² +f ₄ ²)/|f ₂|<3.6  (9)

where,

f₂ is a focal length of the second lens unit,

f₃ is a focal length of the third lens unit, and

f₄ is a focal length of the fourth lens unit.

The condition (9) sets forth the focal lengths of the lens units. Whenthe value exceeds the upper limit of the condition (9), the absolutevalue of the optical power of the second lens unit is relatively strongexcessively. Thus, compensation of various kinds of aberration,especially, compensation of distortion at a wide-angle limit, becomesdifficult. Thus, this situation is not preferable. In contrast, when thevalue goes below the lower limit of the condition (9), the absolutevalue of the optical power of the second lens unit is relatively weakexcessively. Thus, in a case that a zoom lens system having a highmagnification is to be achieved, the necessary amount of movement of thesecond lens unit is excessively great. Thus, this situation is notpreferable.

Here, when at least one of the following conditions (9)′ and (9)″ issatisfied, the above-mentioned effect is achieved more successfully.

2.8<√(f ₃ ² +f ₄ ²)/|f ₂|  (9)′

√(f ₃ ² +f ₄ ²)/|f ₂|<3.5  (9)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (10) is satisfied.

1.95<m _(2T) /m _(34T)<3.47  (10)

where,

m_(2T) is a lateral magnification of the second lens unit at a telephotolimit, and

m_(34T) is a lateral magnification at a telephoto limit of a compositelens unit consisting of all lens units located on the image siderelative to the second lens unit.

The condition (10) sets forth the magnification of the lens units at atelephoto limit. When the value exceeds the upper limit of the condition(10), the overall length at a telephoto limit is excessively great, andhence difficulty arises in realizing a compact zoom lens system.Further, for example, in a case that the lens units on the image siderelative to the second lens unit are moved in a direction perpendicularto the optical axis so that blur compensation is achieved, anexcessively large aberration fluctuation is caused. Thus, this situationis not preferable. In contrast, when the value goes below the lowerlimit of the condition (10), similarly, for example, in a case that thelens units on the image side relative to the second lens unit are movedin a direction perpendicular to the optical axis so that blurcompensation is achieved, an excessively large aberration fluctuation iscaused. Thus, this situation is not preferable.

Here, when at least one of the following conditions (10)′ and (10)″ issatisfied, the above-mentioned effect is achieved more successfully.

2.2<m _(2T) /m _(34T)  (10)′

m _(2T) /m _(34T)<3.2  (10)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (III-11) is satisfied.

0.037<d1NG/d1G<0.135  (I•II-11)

where,

d1NG is an optical axial center thickness of the lens element havingnegative optical power contained in the first lens unit, and

d1G is an optical axial center thickness of the first lens unit.

The condition (III-11) sets forth the thickness of the lens elementhaving negative optical power contained in the first lens unit. When thevalue exceeds the upper limit of the condition (I•II-11), the thicknessof the entirety of the first lens unit is excessively great, and henceit is difficult to achieve a compact zoom lens system. Thus, thissituation is not preferable. In contrast, when the value goes below thelower limit of the condition (I•II-11), remarkable difficulty arises infabricating the lens element having negative optical power contained inthe first lens unit. Thus, this situation is not preferable.

Here, when at least one of either condition (I•II-11)′ or condition(I•II-11)″ and condition (I•II-11)″ is satisfied, the above-mentionedeffect is achieved more successfully.

0.075<d1NG/d1G  (I•II-11)′

0.100<d1NG/d1G  (I•II-11)′

d1NG/d1G<0.110  (I•II-11)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (12) is satisfied.

0.11<f _(W)·tan(ω−ω₀)<0.15  (12)

where,

f_(W) is a focal length of the entire system at a wide-angle limit,

ω is a half view angle (real half view angle (°)) at a wide-angle limit,and

ω₀ is a paraxial half view angle (°) at a wide-angle limit.

The condition (12) sets forth the difference between the real half viewangle and the paraxial half view angle at a wide-angle limit. Thiscondition substantially controls distortion. When the value fallsoutside the range of the condition (12), distortion is excessivelygreat. Thus, this situation is not preferable.

Here, when at least one of the following conditions (12)′ and (12)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.12<f _(W)·tan(ω−ω₀)  (12)′

f _(W)·tan(ω−ω₀)<0.14  (12)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (13) is satisfied.

0.17<f ₄ /f _(T)<0.30  (13)

where,

f₄ is a focal length of the fourth lens unit, and

f_(T) is a focal length of the entire system at a telephoto limit.

The condition (13) sets forth the optical power of the fourth lens unit.When the value exceeds the upper limit of the condition (13), the focallength of the fourth lens unit is excessively long, that is, the opticalpower is excessively weak. Thus, difficulty arises in appropriatelycontrolling the exit pupil position especially at a wide-angle limit.Accordingly, it is difficult in some cases to achieve a satisfactoryimage surface illuminance. In contrast, when the value goes below thelower limit of the condition (13), the focal length of the fourth lensunit is excessively short, that is, the optical power is excessivelystrong. Thus, it becomes difficult that large aberration generated inthe fourth lens unit is compensated by other lens units. Thus, thissituation is not preferable.

Here, when at least one of the following conditions (13)′ and (13)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.19<f ₄ /f _(T)  (13)′

f ₄ /f _(T)<0.26  (13)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (14) is satisfied.

0.60<|M ₁ /M ₂|<1.30  (14)

where,

M₁ is an amount of movement of the first lens unit in the optical axisdirection during zooming from a wide-angle limit to a telephoto limit(movement from the image side to the object side is defined to bepositive), and

M₂ is an amount of movement of the second lens unit in the optical axisdirection during zooming from a wide-angle limit to a telephoto limit(movement from the image side to the object side is defined to bepositive).

The condition (14) sets forth the amount of movement of the first lensunit in the optical axis direction. When the value exceeds the upperlimit of the condition (14), the amount of movement of the first lensunit is excessively large. Thus, the effective diameter of the firstlens unit necessary for achieving a satisfactory F-number at awide-angle limit increases. This causes difficulty in some cases inachieving a compact zoom lens system. In contrast, when the value goesbelow the lower limit of the condition (14), the amount of movement ofthe second lens unit necessary for achieving a satisfactory highmagnification is relatively large excessively. Thus, it is difficult insome cases to achieve a compact zoom lens system.

Here, when at least one of the following conditions (14)′ and (14)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.75<|M ₁ /M ₂|  (14)

|M ₁ /M ₂|<1.15  (14)

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (15) is satisfied.

0.4<|M ₃ /M ₂|<1.2  (15)

where,

M₂ is an amount of movement of the second lens unit in the optical axisdirection during zooming from a wide-angle limit to a telephoto limit(movement from the image side to the object side is defined to bepositive), and

M₃ is an amount of movement of the third lens unit in the optical axisdirection during zooming from a wide-angle limit to a telephoto limit(movement from the image side to the object side is defined to bepositive).

The condition (15) sets forth the amount of movement of the third lensunit in the optical axis direction. When the value exceeds the upperlimit of the condition (15), the amount of movement of the third lensunit is excessively large. Thus, an excessively large aberrationfluctuation is generated in the third lens unit during zooming.Accordingly, it is difficult in some cases to compensate this aberrationby other lens units. In contrast, when the value goes below the lowerlimit of the condition (15), the amount of movement of the third lensunit is excessively small. Thus, a relatively excessively large amountof movement of the second lens unit is necessary for achieving a highmagnification. Accordingly, it is difficult in some cases to achieve acompact zoom lens system.

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (16) is satisfied.

0.35<(m _(2T) /m _(2W))/(f _(T) /f _(W))<0.65  (16)

where,

m_(2T) is a lateral magnification of the second lens unit at a telephotolimit,

m_(2W) is a lateral magnification of the second lens unit at awide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (16) sets forth a lateral magnification change in thesecond lens unit and substantially sets forth the degree of variablemagnification load to the second lens unit. When the value exceeds theupper limit of the condition (16), the variable magnification load tothe second lens unit is excessive. Thus, it is difficult in some casesto compensate various kinds of off-axial aberration, especially,distortion at a wide-angle limit. In contrast, when the value goes belowthe lower limit of the condition (16), the variable magnification loadto the second lens unit is excessively small. Thus, the amount ofmovement of the third lens unit during zooming necessary for achieving asatisfactory high magnification becomes relatively large. Accordingly,it is difficult in some cases to achieve size reduction of the entirezoom lens system.

Here, when at least one of the following conditions (16)′ and (16)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.40<(m _(2T) /m _(2W))/(f _(T) /f _(W))  (16)′

(m _(2T) /m _(2W))/(f _(T) /f _(W))<0.50  (16)

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (17) is satisfied.

1.3<m _(3T) /m _(3W)<2.2  (17)

where,

m_(3T) is a lateral magnification of the third lens unit at a telephotolimit, and

m_(3W) is a lateral magnification of the third lens unit at a wide-anglelimit.

The condition (17) sets forth a lateral magnification change in thethird lens unit and substantially sets forth the degree of variablemagnification load to the third lens unit. When the value exceeds theupper limit of the condition (17), the variable magnification load tothe third lens unit is excessive. Thus, difficulty arises incompensating various kinds of aberration that vary during magnificationchange, especially, in compensating off-axial aberration. Thus, thissituation is not preferable. In contrast, when the value goes below thelower limit of the condition (17), the variable magnification load tothe third lens unit is excessively small. Thus, a relatively excessivelylarge amount of movement of the second lens unit is necessary forachieving a high magnification. Accordingly, it is difficult in somecases to achieve a compact zoom lens system.

Here, when at least one of the following conditions (17)′ and (17)″ issatisfied, the above-mentioned effect is achieved more successfully.

1.5<m _(3T) /m _(3W)  (17)′

m _(3T) /m _(3W)<2.0  (17)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (18) is satisfied.

5.5<√(f ₃ ² +f ₄ ²)/(f _(W)·tan ω)<9.0  (18)

where,

ω is a half view angle (°) at a wide-angle limit,

f₃ is a focal length of the third lens unit,

f₄ is a focal length of the fourth lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (18) sets forth the focal lengths of the third lens unitand the fourth lens unit. When the value exceeds the upper limit of thecondition (18), the focal lengths of the third lens unit and the fourthlens unit are excessively long. This causes difficulty in some cases inachieving a compact zoom lens system. In contrast, when the value goesbelow the lower limit of the condition (18), the focal lengths of thethird lens unit and the fourth lens unit are excessively short. Thus,aberration compensation capability especially of the third lens unit isexcessive. Accordingly, it is difficult in some cases to achievesatisfactory balance of aberration compensation in the entire zoom lenssystem.

Here, when at least one of the following conditions (18)′ and (18)″ issatisfied, the above-mentioned effect is achieved more successfully.

6.8<√(f ₃ ² +f ₄ ²)/(f _(W)·tan ω)  (18)′

√(f ₃ ² +f ₄ ²)/(f _(W)·tan ω)<7.5  (18)

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (19) is satisfied.

3.0<(L _(T) −L _(W))/(f _(W)·tan ω)<6.0  (19)

where,

ω is a half view angle (°) at a wide-angle limit,

L_(T) is an overall optical axial length of the entire system at atelephoto limit (a distance from the most object side surface to themost image side surface),

L_(W) is an overall optical axial length of the entire system at awide-angle limit (a distance from the most object side surface to themost image side surface), and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (19) sets forth an overall length change during zooming.When the value falls outside the range of the condition (19), it isdifficult to construct a compact lens barrel mechanism. Thus, thissituation is not preferable.

Here, when at least one of the following conditions (19)′ and (19)″ issatisfied, the above-mentioned effect is achieved more successfully.

3.5<(L _(T) −L _(W))/(f _(W)·tan ω)  (19)′

(L _(T) −L _(W))/(f _(W)·tan ω)<4.5  (19)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (20) is satisfied.

50<(L _(T) ·f _(T))/f ₄(f _(W)·tan ω)<150  (20)

where,

ω is a half view angle (°) at a wide-angle limit,

L_(T) is an overall optical axial length of the entire system at atelephoto limit (a distance from the most object side surface to themost image side surface),

f₄ is a focal length of the fourth lens unit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (20) sets forth a suitable overall length at a telephotolimit. When the value exceeds the upper limit of the condition (20), theoverall length at a telephoto limit is excessively long, and hence it isdifficult in some cases to achieve a compact zoom lens system having ashort overall length. Further, when the value exceeds the upper limit ofthe condition (20), the overall length at a telephoto limit isexcessively long. Thus, it becomes difficult to construct a compact lensbarrel mechanism. Accordingly, this situation is not preferable. Incontrast, when the value goes below the lower limit of the condition(20), the focal length of the fourth lens unit is, relatively,excessively long. Thus, it becomes difficult to control the exit pupilposition at a wide-angle limit. Accordingly, it becomes difficult tomaintain an appropriate image surface illuminance. Thus, this situationis not preferable.

Here, when at least one of the following conditions (20)′ and (20)″ issatisfied, the above-mentioned effect is achieved more successfully.

80<(L _(T) ·f _(T))/f ₄(f _(W)·tan ω)  (20)′

(L _(T) ·f _(T))/f ₄(f _(W)·tan ω)<125  (20)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (21) is satisfied.

50<(L _(W) ·f _(T))/f ₄(f _(W)·tan ω)<125  (21)

where,

ω is a half view angle (°) at a wide-angle limit,

L_(W) is an overall optical axial length of the entire system at awide-angle limit (a distance from the most object side surface to themost image side surface),

f₄ is a focal length of the fourth lens unit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (21) sets forth a suitable overall length at a wide-anglelimit. When the value exceeds the upper limit of the condition (21), theoverall length at a wide-angle limit is excessively long, and hence itis difficult in some cases to achieve a zoom lens system having acompact accommodation size. In contrast, when the value goes below thelower limit of the condition (21), the focal length of the fourth lensunit is, relatively, excessively long. Thus, it becomes difficult tocontrol the exit pupil position at a wide-angle limit. Accordingly, itbecomes difficult to maintain an appropriate image surface illuminance.Thus, this situation is not preferable.

Here, when at least one of the following conditions (21)′ and (21)″ issatisfied, the above-mentioned effect is achieved more successfully.

65<(L _(W) ·f _(T))/f ₄(f _(W)·tan ω)  (21)′

(L _(W) ·f _(T))/f ₄(f _(W)·tan ω)<100  (21)′

In a zoom lens system having the above-mentioned basic configuration Ilike each zoom lens system according to Embodiments I-1 to I-5 or a zoomlens system having the above-mentioned basic configuration II like eachzoom lens system according to Embodiments II-1 to II-5, it is preferablethat the following condition (22) is satisfied.

4.0<f ₃ /f _(W)·tan ω<5.2  (22)

where,

ω is a half view angle (°) at a wide-angle limit,

f₃ is a focal length of the third lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (22) sets forth the focal length of the third lens unit.When the value exceeds the upper limit of the condition (22), the focallength of the third lens unit is excessively long. This causesdifficulty in some cases in achieving a compact zoom lens system.Further, when the value exceeds the upper limit of the condition (22),the necessary amount of movement in a case that, for example, the thirdlens unit is moved in a direction perpendicular to the optical axis forblur compensation becomes excessively large. Thus, this situation is notpreferable. In contrast, when the value goes below the lower limit ofthe condition (22), the focal length of the third lens unit isexcessively short. Thus, the aberration compensation capability of thethird lens unit is excessive, and hence the compensation balance ofvarious kinds of aberration is degraded. This causes difficulty in somecases in achieving a compact zoom lens system.

Here, when at least one of the following conditions (22)′ and (22)″ issatisfied, the above-mentioned effect is achieved more successfully.

4.4<f ₃ /f _(W)·tan ω  (22)′

f ₃ /f _(W)·tan ω<4.8  (22)′

Here, the lens units constituting the zoom lens system of eachembodiment are composed exclusively of refractive type lenses thatdeflect the incident light by refraction (that is, lenses of a type inwhich deflection is achieved at the interface between media each havinga distinct refractive index). However, the lens type is not limited tothis. For example, the lens units may employ diffractive type lensesthat deflect the incident light by diffraction; refractive-diffractivehybrid type lenses that deflect the incident light by a combination ofdiffraction and refraction; or gradient index type lenses that deflectthe incident light by distribution of refractive index in the medium.

Further, in each embodiment, a reflecting surface may be arranged in theoptical path so that the optical path may be bent before, after or inthe middle of the zoom lens system. The bending position may be set upin accordance with the necessity. When the optical path is bentappropriately, the apparent thickness of a camera can be reduced.

Moreover, each embodiment has been described for the case that a planeparallel plate such as an optical low-pass filter is arranged betweenthe last surface of the zoom lens system (the most image side surface ofthe fourth lens unit) and the image surface S. This low-pass filter maybe: a birefringent type low-pass filter made of, for example, a crystalwhose predetermined crystal orientation is adjusted; or a phase typelow-pass filter that achieves required characteristics of opticalcut-off frequency by diffraction.

Embodiments I-6 and II-6

FIG. 16 is a schematic construction diagram of a digital still cameraaccording to Embodiments I-6 and II-6. In FIG. 16, the digital stillcamera comprises: an imaging device having a zoom lens system 1 and animage sensor 2 composed of a CCD; a liquid crystal display monitor 3;and a body 4. The employed zoom lens system 1 is a zoom lens systemaccording to Embodiments I-1 and II-1. In FIG. 16, the zoom lens system1 comprises a first lens unit G1, a second lens unit G2, a diaphragm A,a third lens unit G3 and a fourth lens unit G4. In the body 4, the zoomlens system 1 is arranged on the front side, while the image sensor 2 isarranged on the rear side of the zoom lens system 1. On the rear side ofthe body 4, the liquid crystal display monitor 3 is arranged, while anoptical image of a photographic object generated by the zoom lens system1 is formed on an image surface S.

The lens barrel comprises a main barrel 5, a moving barrel 6 and acylindrical cam 7. When the cylindrical cam 7 is rotated, the first lensunit G1, the second lens unit G2, the third lens unit G3 and the fourthlens unit G4 move to predetermined positions relative to the imagesensor 2, so that magnification change can be achieved ranging from awide-angle limit to a telephoto limit. The fourth lens unit G4 ismovable in an optical axis direction by a motor for focus adjustment.

As such, when the zoom lens system according to Embodiments I-1 and II-1is employed in a digital still camera, a small digital still camera isobtained that has a high resolution and high capability of compensatingthe curvature of field and that has a short overall optical length oflens system at the time of non-use. Here, in the digital still camerashown in FIG. 16, any one of the zoom lens systems according toEmbodiments I-2 to I-5 and II-2 to II-5 may be employed in place of thezoom lens system according to Embodiments I-1 and II-1. Further, theoptical system of the digital still camera shown in FIG. 16 isapplicable also to a digital video camera for moving images. In thiscase, moving images with high resolution can be acquired in addition tostill images.

Further, an imaging device comprising a zoom lens system according toEmbodiments I-1 to I-5 and II-1 to II-5 described above and an imagesensor such as a CCD or a CMOS may be applied to a mobile telephone, aPDA (Personal Digital Assistance), a surveillance camera in asurveillance system, a Web camera, a vehicle-mounted camera or the like.

Embodiments III-1 to III-4

FIG. 17 is a lens arrangement diagram of a zoom lens system according toEmbodiment III-1. FIG. 20 is a lens arrangement diagram of a zoom lenssystem according to Embodiment III-2. FIG. 23 is a lens arrangementdiagram of a zoom lens system according to Embodiment III-3. FIG. 26 isa lens arrangement diagram of a zoom lens system according to EmbodimentIII-4.

FIGS. 17, 20, 23 and 26 show respectively a zoom lens system in aninfinity in-focus condition. In each figure, part (a) shows a lensconfiguration at a wide-angle limit (in the minimum focal lengthcondition: focal length f_(W)), part (b) shows a lens configuration at amiddle position (in an intermediate focal length condition: focal lengthf_(M)=√(f_(W)·f_(T))), and part (c) shows a lens configuration at atelephoto limit (in the maximum focal length condition: focal lengthf_(T)). Further, in each figure, bent arrows provided between part (a)and part (b) are lines obtained by connecting the positions of the lensunits at a wide-angle limit, at a middle position and at a telephotolimit, in order from the top to the bottom. Thus, straight lines areused simply between a wide-angle limit and a middle position and betweena middle position and a telephoto limit. That is, these straight linesdo not indicate the actual motion of the individual lens units.Moreover, in each figure, an arrow provided to a lens unit indicatesfocusing from an infinity in-focus condition to a close-object in-focuscondition, that is, the moving direction at the time of focusing from aninfinity in-focus condition to a close-object in-focus condition.

The zoom lens system according to each embodiment, in order from theobject side to the image side, comprises a first lens unit G1 havingpositive optical power, a second lens unit G2 having negative opticalpower, a third lens unit G3 having positive optical power, and a fourthlens unit G4 having positive optical power. Then, in zooming from awide-angle limit to a telephoto limit, the first lens unit G1, thesecond lens unit G2, the third lens unit G3 and the fourth lens unit G4all move along the optical axis (this lens configuration is referred toas the basic configuration III of Embodiments III-1 to III-4,hereinafter). In the zoom lens system according to each embodiment,these lens units are arranged into a desired optical power arrangement,so that a remarkably high zooming ratio exceeding 16 and high opticalperformance are achieved and still size reduction is realized in theentire lens system.

In FIGS. 17, 20, 23 and 26, an asterisk “*” provided to a particularsurface indicates that the surface is aspheric. Further, in each figure,a symbol (+) or (−) provided to the sign of each lens unit correspondsto the sign of optical power of the lens unit. Moreover, in each figure,the straight line located on the most right-hand side indicates theposition of an image surface S. On the object side relative to the imagesurface S (between the image surface S and the most image side lenssurface of the fourth lens unit G4), a plane parallel plate such as anoptical low-pass filter and a face plate of an image sensor is provided.Moreover, in each figure, a diaphragm A is provided between the mostimage side lens surface of the second lens unit G2 and the most objectside lens surface of the third lens unit G3.

As shown in FIG. 17, in the zoom lens system according to EmbodimentIII-1, the first lens unit G1, in order from the object side to theimage side, comprises: a negative meniscus first lens element L1 withthe convex surface facing the object side; a positive meniscus secondlens element L2 with the convex surface facing the object side; and apositive meniscus third lens element L3 with the convex surface facingthe object side. Among these, the first lens element L1 and the secondlens element L2 are cemented with each other.

In the zoom lens system according to Embodiment III-1, the second lensunit G2, in order from the object side to the image side, comprises: anegative meniscus fourth lens element L4 with the convex surface facingthe object side; a bi-concave fifth lens element L5; and a bi-convexsixth lens element L6.

Further, in the zoom lens system according to Embodiment III-1, thethird lens unit G3, in order from the object side to the image side,comprises: a positive meniscus seventh lens element L7 with the convexsurface facing the object side; a bi-convex eighth lens element L8; anda bi-concave ninth lens element L9. Among these, the eighth lens elementL8 and the ninth lens element L9 are cemented with each other.

Further, in the zoom lens system according to Embodiment III-1, thefourth lens unit G4, in order from the object side to the image side,comprises: a bi-convex tenth lens element L10; and a negative meniscuseleventh lens element L11 with the convex surface facing the image side.The tenth lens element L10 and the eleventh lens element L11 arecemented with each other.

Here, in the zoom lens system according to Embodiment III-1, a planeparallel plate L12 is provided on the object side relative to the imagesurface S (between the image surface S and the eleventh lens elementL11).

In the zoom lens system according to Embodiment III-1, in zooming from awide-angle limit to a telephoto limit, the first lens unit G1 and thethird lens unit G3 move to the object side, while the second lens unitG2 moves to the image side, that is, such that the position at awide-angle limit should be located on the object side relative to theposition at a telephoto limit. Further, the fourth lens unit G4 moveswith locus of a convex to the object side with changing the intervalwith the third lens unit G3.

As shown in FIG. 20, in the zoom lens system according to EmbodimentIII-2, the first lens unit G1, in order from the object side to theimage side, comprises: a negative meniscus first lens element L1 withthe convex surface facing the object side; a positive meniscus secondlens element L2 with the convex surface facing the object side; and apositive meniscus third lens element L3 with the convex surface facingthe object side. Among these, the first lens element L1 and the secondlens element L2 are cemented with each other.

In the zoom lens system according to Embodiment III-2, the second lensunit G2, in order from the object side to the image side, comprises: anegative meniscus fourth lens element L4 with the convex surface facingthe object side; a bi-concave fifth lens element L5; a bi-convex sixthlens element L6; and a negative meniscus seventh lens element L7 withthe convex surface facing the image side. Among these, the sixth lenselement L6 and the seventh lens element L7 are cemented with each other.

Further, in the zoom lens system according to Embodiment III-2, thethird lens unit G3, in order from the object side to the image side,comprises: a bi-convex eighth lens element L8; a bi-convex ninth lenselement L9; and a bi-concave tenth lens element L10. Among these, theninth lens element L9 and the tenth lens element L10 are cemented witheach other.

Further, in the zoom lens system according to Embodiment III-2, thefourth lens unit G4, in order from the object side to the image side,comprises: a bi-convex eleventh lens element L11; and a negativemeniscus twelfth lens element L12 with the convex surface facing theimage side. The eleventh lens element L11 and the twelfth lens elementL12 are cemented with each other.

Here, in the zoom lens system according to Embodiment III-2, a planeparallel plate L13 is provided on the object side relative to the imagesurface S (between the image surface S and the twelfth lens elementL12).

In the zoom lens system according to Embodiment III-2, in zooming from awide-angle limit to a telephoto limit, the first lens unit G1 and thethird lens unit G3 move to the object side, while the second lens unitG2 moves to the image side, that is, such that the position at awide-angle limit should be located on the object side relative to theposition at a telephoto limit. Further, the fourth lens unit G4 moveswith locus of a convex to the object side with changing the intervalwith the third lens unit G3.

As shown in FIG. 23, in the zoom lens system according to EmbodimentIII-3, the first lens unit G1, in order from the object side to theimage side, comprises: a negative meniscus first lens element L1 withthe convex surface facing the object side; a bi-convex second lenselement L2; and a positive meniscus third lens element L3 with theconvex surface facing the object side. Among these, the first lenselement L1 and the second lens element L2 are cemented with each other.

Further, in the zoom lens system according to Embodiment III-3, thesecond lens unit G2, in order from the object side to the image side,comprises: a negative meniscus fourth lens element L4 with the convexsurface facing the object side; a bi-concave fifth lens element L5; abi-convex sixth lens element L6; and a bi-concave seventh lens elementL7. Among these, the sixth lens element L6 and the seventh lens elementL7 are cemented with each other.

Further, in the zoom lens system according to Embodiment III-3, thethird lens unit G3, in order from the object side to the image side,comprises: a positive meniscus eighth lens element L8 with the convexsurface facing the object side; a bi-convex ninth lens element L9; and abi-concave tenth lens element L10. Among these, the ninth lens elementL9 and the tenth lens element L10 are cemented with each other.

Further, in the zoom lens system according to Embodiment III-3, thefourth lens unit G4, in order from the object side to the image side,comprises: a bi-convex eleventh lens element L11; and a negativemeniscus twelfth lens element L12 with the convex surface facing theimage side. The eleventh lens element L11 and the twelfth lens elementL12 are cemented with each other.

Here, in the zoom lens system according to Embodiment III-3, a planeparallel plate L13 is provided on the object side relative to the imagesurface S (between the image surface S and the twelfth lens elementL12).

In the zoom lens system according to Embodiment III-3, in zooming from awide-angle limit to a telephoto limit, the first lens unit G1 and thethird lens unit G3 move to the object side, while the second lens unitG2 moves to the image side, that is, such that the position at awide-angle limit should be located on the object side relative to theposition at a telephoto limit. Further, the fourth lens unit G4 moveswith locus of a convex to the object side with changing the intervalwith the third lens unit G3.

As shown in FIG. 26, in the zoom lens system according to EmbodimentIII-4, the first lens unit G1, in order from the object side to theimage side, comprises: a negative meniscus first lens element L1 withthe convex surface facing the object side; a bi-convex second lenselement L2; and a positive meniscus third lens element L3 with theconvex surface facing the object side. Among these, the first lenselement L1 and the second lens element L2 are cemented with each other.

Further, in the zoom lens system according to Embodiment III-4, thesecond lens unit G2, in order from the object side to the image side,comprises: a negative meniscus fourth lens element L4 with the convexsurface facing the object side; a bi-concave fifth lens element L5; abi-convex sixth lens element L6; and a bi-concave seventh lens elementL7. Among these, the sixth lens element L6 and the seventh lens elementL7 are cemented with each other.

Further, in the zoom lens system according to Embodiment III-4, thethird lens unit G3, in order from the object side to the image side,comprises: a positive meniscus eighth lens element L8 with the convexsurface facing the object side; a bi-convex ninth lens element L9; and abi-concave tenth lens element L10. Among these, the ninth lens elementL9 and the tenth lens element L10 are cemented with each other.

Further, in the zoom lens system according to Embodiment III-4, thefourth lens unit G4, in order from the object side to the image side,comprises: a bi-convex eleventh lens element L11; and a negativemeniscus twelfth lens element L12 with the convex surface facing theimage side. The eleventh lens element L11 and the twelfth lens elementL12 are cemented with each other.

Here, in the zoom lens system according to Embodiment III-4, a planeparallel plate L13 is provided on the object side relative to the imagesurface S (between the image surface S and the twelfth lens elementL12).

In the zoom lens system according to Embodiment III-4, in zooming from awide-angle limit to a telephoto limit, the first lens unit G1 and thethird lens unit G3 move to the object side, while the second lens unitG2 moves to the image side, that is, such that the position at awide-angle limit should be located on the object side relative to theposition at a telephoto limit. Further, the fourth lens unit G4 moveswith locus of a convex to the object side with changing the intervalwith the third lens unit G3.

In the zoom lens system according to each embodiment, in zooming from awide-angle limit to a telephoto limit, the first lens unit G1, thesecond lens unit G2, the third lens unit G3 and the fourth lens unit G4all move along the optical axis. Among these lens units, for example,the third lens unit is moved in a direction perpendicular to the opticalaxis, so that image blur caused by hand blurring, vibration and the likecan be compensated optically.

In the present invention, when the image blur is to be compensatedoptically, the third lens unit moves in a direction perpendicular to theoptical axis as described above, so that image blur is compensated in astate that size increase in the entire zoom lens system is suppressedand a compact construction is realized and that excellent imagingcharacteristics such as small decentering coma aberration anddecentering astigmatism are satisfied.

The following description is given for conditions desired to besatisfied by a zoom lens system having the above-mentioned basicconfiguration III like the zoom lens system according to EmbodimentsIII-1 to III-4. Here, a plurality of preferable conditions are set forthfor the zoom lens system according to each embodiment. A constructionthat satisfies all the plural conditions is most desirable for the zoomlens system. However, when an individual condition is satisfied, a zoomlens system having the corresponding effect can be obtained.

Further, all conditions described below hold only under the followingtwo premise conditions, unless noticed otherwise.

16<f _(T) /f _(W)

ω>35

where,

f_(T) is a focal length of the entire system at a telephoto limit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

ω is a half view angle (°) at a wide-angle limit.

The zoom lens system having the basic configuration III satisfies thefollowing condition (III-11).

0.036<d1NG/d1G<0.140  (III-11)

where,

d1NG is an optical axial center thickness of the lens element havingnegative optical power contained in the first lens unit, and

d1G is an optical axial center thickness of the first lens unit.

The condition (III-11) sets forth the thickness of the lens elementhaving negative optical power contained in the first lens unit. When thevalue exceeds the upper limit of the condition (III-11), the thicknessof the entirety of the first lens unit is excessively great, and hence acompact zoom lens system is not achieved. In contrast, when the valuegoes below the lower limit of the condition (III-11), the lens elementhaving negative optical power contained in the first lens unit cannot befabricated.

Here, when at least any one of the following condition (III-11)′ or(III-11)″ and the following condition (III-11)′″ or (III-11)″″ issatisfied, the above-mentioned effect is achieved more successfully.

0.075<d1NG/d1G  (III-11)′

0.100<d1NG/d1G  (III-11)′

d1NG/d1G<0.135  (III-11)

d1NG/d1G<0.110  (III-11)

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (1) is satisfied.

0<√/(f ₄ ·f _(W)·tan ω)/L _(W)<0.13  (1)

where,

ω is a half view angle (°) at a wide-angle limit,

L_(W) is an overall optical axial length of the entire system at awide-angle limit (a distance from the most object side surface to themost image side surface),

f₄ is a focal length of the fourth lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (1) substantially sets forth the focal length of thefourth lens unit. When the value exceeds the upper limit of thecondition (1), the optical power of the fourth lens unit is excessivelyweak, and hence the necessary amount of movement in zooming increases.Thus, it is difficult in some cases to achieve a thin lens barrelconfiguration. This situation is not preferable. Further, when the valueexceeds the upper limit of the condition (1), it becomes difficult insome cases to achieve a satisfactory peripheral illuminance on the imagesurface especially at a wide-angle limit.

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (2) is satisfied.

0.05≦f ₃ /f ₄≦0.97  (2)

where,

f₃ is a focal length of the third lens unit, and

f₄ is a focal length of the fourth lens unit.

The condition (2) sets forth the ratio between the focal length of thethird lens unit and the focal length of the fourth lens unit. When thevalue exceeds the upper limit of the condition (2), the focal length ofthe third lens unit is excessively long. Thus, a possibility arises thatthe amount of movement of the third lens unit necessary for achieving ahigh magnification exceeding 16 increases excessively. Further, when thevalue exceeds the upper limit of the condition (2), in some cases, itbecomes difficult that, for example, the third lens unit is moved in adirection perpendicular to the optical axis for blur compensation. Incontrast, when the value goes below the lower limit of the condition(2), the focal length of the third lens unit is excessively short. Thus,a large aberration fluctuation arises in zooming so as to causedifficulty in compensation. Further, the absolute values of variouskinds of aberration generated in the third lens unit increaseexcessively, and hence compensation becomes difficult. Thus, thissituation is not preferable. Moreover, when the value goes below thelower limit of the condition (2), an excessively high error sensitivityto the inclination between the surfaces in the third lens unit iscaused. This causes in some cases difficulty in assembling the opticalsystem.

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4,especially in a case that the second lens unit includes a lens elementhaving negative optical power and being arranged on the most object sideand a lens element having positive optical power, it is preferable thatthe following condition (3) is satisfied.

(nd ₄−1)+(nd ₆−1)≧1.8  (3)

where,

nd₄ is a refractive index to the d-line of a lens element havingnegative optical power and being arranged on the most object side in thesecond lens unit, and

nd₆ is a refractive index to the d-line of a lens element havingpositive optical power in the second lens unit.

The condition (3) sets forth a condition desired to be satisfied by lenselements contained in the second lens unit. When the value falls outsidethe range of the condition (3), compensation of distortion and curvatureof field is difficult especially at a wide-angle limit. Thus, thissituation is not preferable.

Here, when the following condition (3)′ is satisfied, theabove-mentioned effect is achieved more successfully.

(nd ₄−1)+(nd ₆−1)≧1.9  (3)

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (8) is satisfied.

0.15<dG3/dG<0.27  (8)

where,

dG3 is an optical axial center thickness of the third lens unit, and

dG is a sum of the optical axial thicknesses of the first lens unit, thesecond lens unit, the third lens unit and the fourth lens unit.

The condition (8) sets forth the optical axial thickness of the thirdlens unit. When the value exceeds the upper limit of the condition (8),the thickness of the third lens unit is excessively great, and hence itis difficult in some cases to achieve a compact lens system. Further,when the value exceeds the upper limit of the condition (8), thethickness of the third lens unit is excessively great, and hence itbecomes difficult that, for example, the third lens unit is moved in adirection perpendicular to the optical axis for blur compensation. Incontrast, when the value goes below the lower limit of the condition(8), difficulty arises in compensating various kinds of aberration to becompensated by the third lens unit, especially in compensating sphericalaberration and coma aberration at a wide-angle limit. Thus, thissituation is not preferable.

Here, when at least one of the following conditions (8)′ and (8)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.19<dG3/dG  (8)′

dG3/dG<0.22  (8)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (9) is satisfied.

2.7<√(f ₃ ² +f ₄ ²)/|f ₂|<3.6  (9)

where,

f₂ is a focal length of the second lens unit,

f₃ is a focal length of the third lens unit, and

f₄ is a focal length of the fourth lens unit.

The condition (9) sets forth the focal lengths of the lens units. Whenthe value exceeds the upper limit of the condition (9), the absolutevalue of the optical power of the second lens unit is relatively strongexcessively. Thus, compensation of various kinds of aberration,especially, compensation of distortion at a wide-angle limit, becomesdifficult. Thus, this situation is not preferable. In contrast, when thevalue goes below the lower limit of the condition (9), the absolutevalue of the optical power of the second lens unit is relatively weakexcessively. Thus, in a case that a zoom lens system having a highmagnification is to be achieved, the necessary amount of movement of thesecond lens unit is excessively great. Thus, this situation is notpreferable.

Here, when at least one of the following conditions (9)′ and (9)″ issatisfied, the above-mentioned effect is achieved more successfully.

2.8<√(f ₃ ² +f ₄ ²)/|f ₂|  (9)′

√(f ₃ ² +f ₄ ²)/|f ₂|<3.5  (9)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (10) is satisfied.

1.95<m _(2T) /m _(34T)<3.47  (10)

where,

m_(2T) is a lateral magnification of the second lens unit at a telephotolimit, and

m_(34T) is a lateral magnification at a telephoto limit of a compositelens unit consisting of all lens units located on the image siderelative to the second lens unit.

The condition (10) sets forth the magnification of the lens units at atelephoto limit. When the value exceeds the upper limit of the condition(10), the overall length at a telephoto limit is excessively great, andhence difficulty arises in realizing a compact zoom lens system.Further, for example, in a case that the lens units on the image siderelative to the second lens unit are moved in a direction perpendicularto the optical axis so that blur compensation is achieved, anexcessively large aberration fluctuation is caused. Thus, this situationis not preferable. In contrast, when the value goes below the lowerlimit of the condition (10), similarly, for example, in a case that thelens units on the image side relative to the second lens unit are movedin a direction perpendicular to the optical axis so that blurcompensation is achieved, an excessively large aberration fluctuation iscaused. Thus, this situation is not preferable.

Here, when at least one of the following conditions (10)′ and (10)″ issatisfied, the above-mentioned effect is achieved more successfully.

2.2<m _(2T) /m _(34T)  (10)′

m _(2T) /m _(34T)<3.2  (10)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (12) is satisfied.

0.11<f _(W)′tan(ω−ω₀)<0.15  (12)

where,

f_(W) is a focal length of the entire system at a wide-angle limit,

ω is a half view angle (real half view angle (°)) at a wide-angle limit,and

ω₀ is a paraxial half view angle (°) at a wide-angle limit.

The condition (12) sets forth the difference between the real half viewangle and the paraxial half view angle at a wide-angle limit. Thiscondition substantially controls distortion. When the value fallsoutside the range of the condition (12), distortion is excessivelygreat. Thus, this situation is not preferable.

Here, when at least one of the following conditions (12)′ and (12)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.12<f _(W)·tan(ω−ω₀)  (12)′

f _(W)·tan(ω−ω₀)<0.14  (12)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (13) is satisfied.

0.17<f ₄ /f _(T)<0.30  (13)

where,

f₄ is a focal length of the fourth lens unit, and

f_(T) is a focal length of the entire system at a telephoto limit.

The condition (13) sets forth the optical power of the fourth lens unit.When the value exceeds the upper limit of the condition (13), the focallength of the fourth lens unit is excessively long, that is, the opticalpower is excessively weak. Thus, difficulty arises in appropriatelycontrolling the exit pupil position especially at a wide-angle limit.Accordingly, it is difficult in some cases to achieve a satisfactoryimage surface illuminance. In contrast, when the value goes below thelower limit of the condition (13), the focal length of the fourth lensunit is excessively short, that is, the optical power is excessivelystrong. Thus, it becomes difficult that large aberration generated inthe fourth lens unit is compensated by other lens units. Thus, thissituation is not preferable.

Here, when at least one of the following conditions (13)′ and (13)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.19<f ₄ /f _(T)  (13)′

f ₄ /f _(T)<0.26  (13)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (14) is satisfied.

0.60<|M ₁ /M ₂|<1.30  (14)

where,

M₁ is an amount of movement of the first lens unit in the optical axisdirection during zooming from a wide-angle limit to a telephoto limit(movement from the image side to the object side is defined to bepositive), and

M₂ is an amount of movement of the second lens unit in the optical axisdirection during zooming from a wide-angle limit to a telephoto limit(movement from the image side to the object side is defined to bepositive).

The condition (14) sets forth the amount of movement of the first lensunit in the optical axis direction. When the value exceeds the upperlimit of the condition (14), the amount of movement of the first lensunit is excessively large. Thus, the effective diameter of the firstlens unit necessary for achieving a satisfactory F-number at awide-angle limit increases. This causes difficulty in some cases inachieving a compact zoom lens system. In contrast, when the value goesbelow the lower limit of the condition (14), the amount of movement ofthe second lens unit necessary for achieving a satisfactory highmagnification is relatively large excessively. Thus, it is difficult insome cases to achieve a compact zoom lens system.

Here, when at least one of the following conditions (14)′ and (14)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.75<|M ₁ /M ₂|  (14)′

|M ₁ /M ₂|<1.15  (14)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (15) is satisfied.

0.4<|M ₃ /M ₂|<1.2  (15)

where,

M₂ is an amount of movement of the second lens unit in the optical axisdirection during zooming from a wide-angle limit to a telephoto limit(movement from the image side to the object side is defined to bepositive), and

M₃ is an amount of movement of the third lens unit in the optical axisdirection during zooming from a wide-angle limit to a telephoto limit(movement from the image side to the object side is defined to bepositive).

The condition (15) sets forth the amount of movement of the third lensunit in the optical axis direction. When the value exceeds the upperlimit of the condition (15), the amount of movement of the third lensunit is excessively large. Thus, an excessively large aberrationfluctuation is generated in the third lens unit during zooming.Accordingly, it is difficult in some cases to compensate this aberrationby other lens units. In contrast, when the value goes below the lowerlimit of the condition (15), the amount of movement of the third lensunit is excessively small. Thus, a relatively excessively large amountof movement of the second lens unit is necessary for achieving a highmagnification. Accordingly, it is difficult in some cases to achieve acompact zoom lens system.

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (16) is satisfied.

0.35<(m _(2T) /m _(2W))/(f _(T) /f _(W))<0.65  (16)

where,

m_(2T) is a lateral magnification of the second lens unit at a telephotolimit,

m_(2W) is a lateral magnification of the second lens unit at awide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (16) sets forth a lateral magnification change in thesecond lens unit and substantially sets forth the degree of variablemagnification load to the second lens unit. When the value exceeds theupper limit of the condition (16), the variable magnification load tothe second lens unit is excessive. Thus, it is difficult in some casesto compensate various kinds of off-axial aberration, especially,distortion at a wide-angle limit. In contrast, when the value goes belowthe lower limit of the condition (16), the variable magnification loadto the second lens unit is excessively small. Thus, the amount ofmovement of the third lens unit during zooming necessary for achieving asatisfactory high magnification becomes relatively large. Accordingly,it is difficult in some cases to achieve size reduction of the entirezoom lens system.

Here, when at least one of the following conditions (16)′ and (16)″ issatisfied, the above-mentioned effect is achieved more successfully.

0.40<(m _(2T) /m _(2W))/(f _(T) /f _(W))  (16)′

(m _(2T) /m _(2W))/(f _(T) /f _(W))<0.50  (16)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (17) is satisfied.

1.3<m _(3T) /m _(3W)<2.2  (17)

where,

m_(3T) is a lateral magnification of the third lens unit at a telephotolimit, and

m_(3W) is a lateral magnification of the third lens unit at a wide-anglelimit.

The condition (17) sets forth a lateral magnification change in thethird lens unit and substantially sets forth the degree of variablemagnification load to the third lens unit. When the value exceeds theupper limit of the condition (17), the variable magnification load tothe third lens unit is excessive. Thus, difficulty arises incompensating various kinds of aberration that vary during magnificationchange, especially, in compensating off-axial aberration. Thus, thissituation is not preferable. In contrast, when the value goes below thelower limit of the condition (17), the variable magnification load tothe third lens unit is excessively small. Thus, a relatively excessivelylarge amount of movement of the second lens unit is necessary forachieving a high magnification. Accordingly, it is difficult in somecases to achieve a compact zoom lens system.

Here, when at least one of the following conditions (17)′ and (17)″ issatisfied, the above-mentioned effect is achieved more successfully.

1.5<m _(3T) /m _(3W)  (17)′

m _(3T) /m _(3W)<2.0  (17)

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (18) is satisfied.

5.5<√(f ₃ ² +f ₄ ²)/(f _(w)·tan ω)<9.0  (18)

where,

ω is a half view angle (°) at a wide-angle limit,

f₃ is a focal length of the third lens unit,

f₄ is a focal length of the fourth lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (18) sets forth the focal lengths of the third lens unitand the fourth lens unit. When the value exceeds the upper limit of thecondition (18), the focal lengths of the third lens unit and the fourthlens unit are excessively long. This causes difficulty in some cases inachieving a compact zoom lens system. In contrast, when the value goesbelow the lower limit of the condition (18), the focal lengths of thethird lens unit and the fourth lens unit are excessively short. Thus,aberration compensation capability especially of the third lens unit isexcessive. Accordingly, it is difficult in some cases to achievesatisfactory balance of aberration compensation in the entire zoom lenssystem.

Here, when at least one of the following conditions (18)′ and (18)″ issatisfied, the above-mentioned effect is achieved more successfully.

6.8<√(f ₃ ² +f ₄ ²)/(f _(W)·tan ω)  (18)′

√(f ₃ ² +f ₄ ²)/(f _(W)·tan ω)<7.5  (18)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (19) is satisfied.

3.0<(L _(T) −L _(W))/(f _(W)·tan ω)<6.0  (19)

where,

ω is a half view angle (°) at a wide-angle limit,

L_(T) is an overall optical axial length of the entire system at atelephoto limit (a distance from the most object side surface to themost image side surface),

L_(W) is an overall optical axial length of the entire system at awide-angle limit (a distance from the most object side surface to themost image side surface), and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (19) sets forth an overall length change during zooming.When the value falls outside the range of the condition (19), it isdifficult to construct a compact lens barrel mechanism. Thus, thissituation is not preferable.

Here, when at least one of the following conditions (19)′ and (19)″ issatisfied, the above-mentioned effect is achieved more successfully.

3.5<(L _(T) −L _(W))/(f _(W)·tan ω)  (19)′

(L _(T) −L _(W))/(f _(W)·tan ω)<4.5  (19)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (20) is satisfied.

50<(L _(T) ·f _(T))/f ₄(f _(W)·tan ω)<150  (20)

where,

ω is a half view angle (°) at a wide-angle limit,

L_(T) is an overall optical axial length of the entire system at atelephoto limit (a distance from the most object side surface to themost image side surface),

f₄ is a focal length of the fourth lens unit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (20) sets forth a suitable overall length at a telephotolimit. When the value exceeds the upper limit of the condition (20), theoverall length at a telephoto limit is excessively long, and hence it isdifficult in some cases to achieve a compact zoom lens system having ashort overall length. Further, when the value exceeds the upper limit ofthe condition (20), the overall length at a telephoto limit isexcessively long. Thus, it becomes difficult to construct a compact lensbarrel mechanism. Accordingly, this situation is not preferable. Incontrast, when the value goes below the lower limit of the condition(20), the focal length of the fourth lens unit is, relatively,excessively long. Thus, it becomes difficult to control the exit pupilposition at a wide-angle limit. Accordingly, it becomes difficult tomaintain an appropriate image surface illuminance. Thus, this situationis not preferable.

Here, when at least one of the following conditions (20)′ and (20)″ issatisfied, the above-mentioned effect is achieved more successfully.

80<(L _(T) ·f _(T))/f ₄(f _(W)·tan ω)  (20)′

(L _(T) ·f _(T))/f ₄(f _(W)·tan ω)<125  (20)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (21) is satisfied.

50<(L _(W) ·f _(T))/f ₄(f _(W)·tan ω)<125  (21)

where,

ω is a half view angle (°) at a wide-angle limit,

L_(W) is an overall optical axial length of the entire system at awide-angle limit (a distance from the most object side surface to themost image side surface),

f₄ is a focal length of the fourth lens unit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (21) sets forth a suitable overall length at a wide-anglelimit. When the value exceeds the upper limit of the condition (21), theoverall length at a wide-angle limit is excessively long, and hence itis difficult in some cases to achieve a zoom lens system having acompact accommodation size. In contrast, when the value goes below thelower limit of the condition (21), the focal length of the fourth lensunit is, relatively, excessively long. Thus, it becomes difficult tocontrol the exit pupil position at a wide-angle limit. Accordingly, itbecomes difficult to maintain an appropriate image surface illuminance.Thus, this situation is not preferable.

Here, when at least one of the following conditions (21)′ and (21)″ issatisfied, the above-mentioned effect is achieved more successfully.

65<(L _(W) ·f _(T))/f ₄(f _(W)·tan ω)  (21)′

(L _(W) ·f _(T))/f ₄(f _(W)·tan ω)<100  (21)′

In a zoom lens system having the above-mentioned basic configuration IIIlike each zoom lens system according to Embodiments III-1 to III-4, itis preferable that the following condition (22) is satisfied.

4.0<f ₃ /f _(W)·tan ω<5.2  (22)

where,

ω is a half view angle (°) at a wide-angle limit,

f₃ is a focal length of the third lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (22) sets forth the focal length of the third lens unit.When the value exceeds the upper limit of the condition (22), the focallength of the third lens unit is excessively long. This causesdifficulty in some cases in achieving a compact zoom lens system.Further, when the value exceeds the upper limit of the condition (22),the necessary amount of movement in a case that, for example, the thirdlens unit is moved in a direction perpendicular to the optical axis forblur compensation becomes excessively large. Thus, this situation is notpreferable. In contrast, when the value goes below the lower limit ofthe condition (22), the focal length of the third lens unit isexcessively short. Thus, the aberration compensation capability of thethird lens unit is excessive, and hence the compensation balance ofvarious kinds of aberration is degraded. This causes difficulty in somecases in achieving a compact zoom lens system.

Here, when at least one of the following conditions (22)′ and (22)″ issatisfied, the above-mentioned effect is achieved more successfully.

4.4<f ₃ /f _(W)·tan ω  (22)′

f ₃ /f _(W)·tan ω<4.8  (22)′

Here, the lens units constituting the zoom lens system of eachembodiment are composed exclusively of refractive type lenses thatdeflect the incident light by refraction (that is, lenses of a type inwhich deflection is achieved at the interface between media each havinga distinct refractive index). However, the lens type is not limited tothis. For example, the lens units may employ diffractive type lensesthat deflect the incident light by diffraction; refractive-diffractivehybrid type lenses that deflect the incident light by a combination ofdiffraction and refraction; or gradient index type lenses that deflectthe incident light by distribution of refractive index in the medium.

Further, in each embodiment, a reflecting surface may be arranged in theoptical path so that the optical path may be bent before, after or inthe middle of the zoom lens system. The bending position may be set upin accordance with the necessity. When the optical path is bentappropriately, the apparent thickness of a camera can be reduced.

Moreover, each embodiment has been described for the case that a planeparallel plate such as an optical low-pass filter is arranged betweenthe last surface of the zoom lens system (the most image side surface ofthe fourth lens unit) and the image surface S. This low-pass filter maybe: a birefringent type low-pass filter made of, for example, a crystalwhose predetermined crystal orientation is adjusted; or a phase typelow-pass filter that achieves required characteristics of opticalcut-off frequency by diffraction.

Embodiment III-5

FIG. 29 is a schematic construction diagram of a digital still cameraaccording to Embodiment III-5. In FIG. 29, the digital still cameracomprises: an imaging device having a zoom lens system 1 and an imagesensor 2 composed of a CCD; a liquid crystal display monitor 3; and abody 4. The employed zoom lens system 1 is a zoom lens system accordingto Embodiment III-1. In FIG. 29, the zoom lens system 1 comprises afirst lens unit G1, a second lens unit G2, a diaphragm A, a third lensunit G3 and a fourth lens unit G4. In the body 4, the zoom lens system 1is arranged on the front side, while the image sensor 2 is arranged onthe rear side of the zoom lens system 1. On the rear side of the body 4,the liquid crystal display monitor 3 is arranged, while an optical imageof a photographic object generated by the zoom lens system 1 is formedon an image surface S.

The lens barrel comprises a main barrel 5, a moving barrel 6 and acylindrical cam 7. When the cylindrical cam 7 is rotated, the first lensunit G1, the second lens unit G2, the third lens unit G3 and the fourthlens unit G4 move to predetermined positions relative to the imagesensor 2, so that magnification change can be achieved ranging from awide-angle limit to a telephoto limit. The fourth lens unit G4 ismovable in an optical axis direction by a motor for focus adjustment.

As such, when the zoom lens system according to Embodiment III-1 isemployed in a digital still camera, a small digital still camera isobtained that has a high resolution and high capability of compensatingthe curvature of field and that has a short overall optical length oflens system at the time of non-use. Here, in the digital still camerashown in FIG. 29, any one of the zoom lens systems according toEmbodiments III-2 to III-4 may be employed in place of the zoom lenssystem according to Embodiment III-1. Further, the optical system of thedigital still camera shown in FIG. 29 is applicable also to a digitalvideo camera for moving images. In this case, moving images with highresolution can be acquired in addition to still images.

Further, an imaging device comprising a zoom lens system according toEmbodiments III-1 to III-4 described above and an image sensor such as aCCD or a CMOS may be applied to a mobile telephone, a PDA (PersonalDigital Assistance), a surveillance camera in a surveillance system, aWeb camera, a vehicle-mounted camera or the like.

Numerical examples are described below in which the zoom lens systemsaccording to Embodiments I-1 to I-5, II-1 to II-5 and III-1 to III-4 areimplemented. In the numerical examples, the units of the length in thetables are all “mm”, while the units of the view angle are all “°”.Moreover, in the numerical examples, r is the radius of curvature, d isthe axial distance, nd is the refractive index to the d-line, and vd isthe Abbe number to the d-line. In the numerical examples, the surfacesmarked with * are aspheric surfaces, and the aspheric surfaceconfiguration is defined by the following expression.

$Z = {\frac{h^{2}/r}{1 + \sqrt{1 - {\left( {1 + \kappa} \right)\left( {h/r} \right)^{2}}}} + {A\; 4h^{4}} + {A\; 6h^{6}} + {A\; 8h^{8}} + {A\; 10h^{10}} + {A\; 12h^{12}}}$

Here, κ is the conic constant, and A4, A6, A8, A10 and A12 are afourth-order, sixth-order, eighth-order, tenth-order and twelfth-orderaspherical coefficients, respectively.

FIG. 2 is a longitudinal aberration diagram of a zoom lens systemaccording to Examples I-1 and II-1. FIG. 5 is a longitudinal aberrationdiagram of a zoom lens system according to Examples I-2 and II-2. FIG. 8is a longitudinal aberration diagram of a zoom lens system according toExamples I-3 and II-3. FIG. 11 is a longitudinal aberration diagram of azoom lens system according to Examples I-4 and II-4. FIG. 14 is alongitudinal aberration diagram of a zoom lens system according toExamples I-5 and II-5.

FIG. 18 is a longitudinal aberration diagram of a zoom lens systemaccording to Example III-1. FIG. 21 is a longitudinal aberration diagramof a zoom lens system according to Example III-2. FIG. 24 is alongitudinal aberration diagram of a zoom lens system according toExample III-3. FIG. 27 is a longitudinal aberration diagram of a zoomlens system according to Example III-4.

In each longitudinal aberration diagram, part (a) shows the aberrationat a wide-angle limit, part (b) shows the aberration at a middleposition, and part (c) shows the aberration at a telephoto limit. Eachlongitudinal aberration diagram, in order from the left-hand side, showsthe spherical aberration (SA (mm)), the astigmatism (AST (mm)) and thedistortion (DIS (%)). In each spherical aberration diagram, the verticalaxis indicates the F-number (in each FIG., indicated as F), and thesolid line, the short dash line and the long dash line indicate thecharacteristics to the d-line, the F-line and the C-line, respectively.In each astigmatism diagram, the vertical axis indicates the imageheight (in each FIG., indicated as H), and the solid line and the dashline indicate the characteristics to the sagittal plane (in each FIG.,indicated as “s”) and the meridional plane (in each FIG., indicated as“m”), respectively. In each distortion diagram, the vertical axisindicates the image height (in each FIG., indicated as H).

Further, FIG. 3 is a lateral aberration diagram at a telephoto limit ofa zoom lens system according to Examples I-1 and II-1. FIG. 6 is alateral aberration diagram at a telephoto limit of a zoom lens systemaccording to Examples I-2 and II-2. FIG. 9 is a lateral aberrationdiagram at a telephoto limit of a zoom lens system according to ExamplesI-3 and II-3. FIG. 12 is a lateral aberration diagram at a telephotolimit of a zoom lens system according to Examples I-4 and II-4. FIG. 15is a lateral aberration diagram at a telephoto limit of a zoom lenssystem according to Examples I-5 and II-5.

Further, FIG. 19 is a lateral aberration diagram at a telephoto limit ofa zoom lens system according to Example III-1. FIG. 22 is a lateralaberration diagram at a telephoto limit of a zoom lens system accordingto Example III-2. FIG. 25 is a lateral aberration diagram at a telephotolimit of a zoom lens system according to Example III-3. FIG. 28 is alateral aberration diagram at a telephoto limit of a zoom lens systemaccording to Example III-4.

In each lateral aberration diagram, the upper three aberration diagramscorrespond to a basic state where image blur compensation is notperformed at a telephoto limit, while the lower three aberrationdiagrams correspond to an image blur compensation state where the entirethird lens unit G3 is moved by a predetermined amount in a directionperpendicular to the optical axis at a telephoto limit. Among thelateral aberration diagrams of the basic state, the upper one shows thelateral aberration at an image point of 70% of the maximum image height,the middle one shows the lateral aberration at the axial image point,and the lower one shows the lateral aberration at an image point of −70%of the maximum image height. Among the lateral aberration diagrams of animage blur compensation state, the upper one shows the lateralaberration at an image point of 70% of the maximum image height, themiddle one shows the lateral aberration at the axial image point, andthe lower one shows the lateral aberration at an image point of −70% ofthe maximum image height. In each lateral aberration diagram, thehorizontal axis indicates the distance from the principal ray on thepupil surface. The solid line indicates the characteristics to thed-line, the short dash line indicates the characteristics to the F-line,and the long dash line indicates the characteristics to the C-line. Ineach lateral aberration diagram, the meridional plane is adopted as theplane containing the optical axis of the first lens unit G1 and theoptical axis of the third lens unit G3.

The amount of movement of the third lens unit G3 in a directionperpendicular to the optical axis in the image blur compensation stateat a telephoto limit is as follows.

Examples I-1 and II-1 0.323 mm

Examples I-2 and II-2 0.295 mm

Examples I-3 and II-3 0.300 mm

Examples I-4 and II-4 0.333 mm

Examples I-5 and II-5 0.338 mm

Example III-1 0.264 mm

Example III-2 0.268 mm

Example III-3 0.295 mm

Example III-4 0.287 mm

When the shooting distance is infinity, at a telephoto limit, the amountof image decentering in a case that the zoom lens system inclines by0.3° is equal to the amount of image decentering in a case that theentire third lens unit G3 displaces in parallel by each of theabove-mentioned values in a direction perpendicular to the optical axis.

As seen from the lateral aberration diagrams, satisfactory symmetry isobtained in the lateral aberration at the axial image point. Further,when the lateral aberration at the +70% image point and the lateralaberration at the −70% image point are compared with each other in thebasic state, all have a small degree of curvature and almost the sameinclination in the aberration curve. Thus, decentering coma aberrationand decentering astigmatism are small. This indicates that sufficientimaging performance is obtained even in the image blur compensationstate. Further, when the image blur compensation angle of a zoom lenssystem is the same, the amount of parallel translation required forimage blur compensation decreases with decreasing focal length of theentire zoom lens system. Thus, at arbitrary zoom positions, sufficientimage blur compensation can be performed for image blur compensationangles up to 0.3° without degrading the imaging characteristics.

Numerical Examples I-1 and II-1

The zoom lens systems of Numerical Examples I-1 and II-1 correspondrespectively to Embodiments I-1 and II-1 shown in FIG. 1. Table I•II-1shows the surface data of the zoom lens systems of Numerical ExamplesI-1 and II-1. Table I•II-2 shows the aspherical data. Table I•II-3 showsvarious data.

TABLE I·II-1 (Surface data) Surface number r d nd vd Object surface ∞ ∞ 1 54.67874 1.15000 2.20000 24.0  2 36.43543 5.05340 1.49700 81.6  3−416.24419 0.15000  4 31.15733 3.57660 1.75161 48.6  5 85.40205 Variable 6 41.03425 0.70000 2.00000 40.0  7 7.60737 4.29990  8* −19.893290.80000 1.72500 54.0  9* 32.70363 0.99640 10 22.93899 1.67400 2.2000024.0 11 −97.37342 0.45000 1.79999 41.7 12 111.71189 Variable 13(Diaphragm) ∞ 1.20000 14 7.49994 1.92750 1.63645 59.1 15 215.917671.69790 16* 9.43190 1.90840 1.69652 42.0 17 −11.33555 0.45000 1.8059530.0 18 5.99424 Variable 19* 12.22671 2.80000 1.50044 69.0 20 −14.833480.45000 1.84700 23.8 21 −22.64524 Variable 22 ∞ 0.78000 1.51680 64.2 23∞ (BF) Image surface ∞

TABLE I·II-2 (Aspherical data) Surface No. 8 K = 0.00000E+00, A4 =3.50052E−04, A6 = −1.20811E−05, A8 = 1.44741E−07 A10 = −1.04598E−09Surface No. 9 K = 0.00000E+00, A4 = 2.88194E−04, A6 = −1.20520E−05, A8 =1.42732E−07 A10 = −6.36269E−10 Surface No. 16 K = 0.00000E+00, A4 =−3.76392E−04, A6 = −5.68479E−06, A8 = −4.59085E−07 A10 = 4.37960E−09Surface No. 19 K = 0.00000E+00, A4 = −5.44658E−05, A6 = 2.12430E−06, A8= −3.55190E−08 A10 = 0.00000E+00

TABLE I·II-3 (Various data) Zooming ratio 17.36563 Wide-angle MiddleTelephoto limit position limit Focal length 4.7524 33.0049 82.5290F-number 2.91648 3.48271 4.34807 View angle 38.5456 6.2523 2.4721 Imageheight 3.6000 3.6000 3.6000 Overall length 73.9059 79.1817 89.0086 oflens system BF 0.87587 0.87107 0.87851 d5 0.6000 26.5565 33.9577 d1230.3658 3.5702 2.1000 d18 6.4260 6.1225 18.5502 d21 5.5741 11.99733.4581 Entrance pupil 18.0226 120.2230 262.6229 position Exit pupil−32.7172 −37.5269 95.6119 position Front principal 22.1027 124.8587417.0488 points position Back principal 69.1534 46.1768 6.4796 pointsposition

Numerical Examples I-2 and II-2

The zoom lens systems of Numerical Examples I-2 and II-2 correspondrespectively to Embodiments I-2 and II-2 shown in FIG. 4. Table I•II-4shows the surface data of the zoom lens systems of Numerical ExamplesI-2 and II-2. Table I•II-5 shows the aspherical data. Table I•II-6 showsvarious data.

TABLE I·II-4 (Surface data) Surface number r d nd vd Object surface ∞ ∞ 1 45.52425 1.30000 1.84666 23.8  2 32.16757 6.00000 1.49700 81.6  3−474.36440 0.15000  4 31.42311 3.20000 1.60311 60.7  5 71.93247 Variable 6 85.97154 0.70000 1.90366 31.3  7 7.78750 4.70000  8* −20.490270.80000 1.66547 55.2  9* 31.55131 0.85000 10 20.49610 2.45000 1.9228620.9 11 −33.70458 0.60000 1.83481 42.7 12 150.07760 Variable 13(Diaphragm) ∞ 2.30000 14 8.35327 1.90000 1.69680 55.5 15 53.324272.25000 16* 9.98413 1.58000 1.66547 55.2 17 −21.94441 0.50000 1.7173629.5 18 6.46504 Variable 19* 13.63884 3.80000 1.60602 57.4 20 −10.923920.60000 1.68893 31.2 21 −48.40053 Variable 22 ∞ 1.50000 1.51633 64.0 23∞ (BF) Image surface ∞

TABLE I·II-5 (Aspherical data) Surface No. 8 K = −6.51516E+00, A4 =1.85470E−04, A6 = −2.94467E−06, A8 = 3.17185E−08 A10 = 9.46754E−10, A12= −4.06466E−11 Surface No. 9 K = 1.96222E+01, A4 = 1.45329E−04, A6 =−5.97511E−06, A8 = 1.32603E−07 A10 = −3.11453E−09, A12 = −4.13309E−12Surface No. 16 K = 0.00000E+00, A4 = −3.49509E−04, A6 = −1.57238E−06, A8= −9.09262E−07 A10 = 4.55753E−08, A12 = 0.00000E+00 Surface No. 19 K =0.00000E+00, A4 = −1.00133E−05, A6 = 1.18861E−06, A8 = −1.20988E−08 A10= 0.00000E+00, A12 = 0.00000E+00

TABLE I·II-6 (Various data) Zooming ratio 20.73116 Wide-angle MiddleTelephoto limit position limit Focal length 4.7135 32.2077 97.7165F-number 2.90061 3.42257 5.05142 View angle 39.0553 6.3899 2.0709 Imageheight 3.6000 3.6000 3.6000 Overall length 76.3557 83.2004 97.3161 oflens system BF 0.36998 0.36997 0.36990 d5 0.6545 25.5533 32.6164 d1228.3328 3.0495 1.3091 d18 5.9770 6.9976 25.9569 d21 5.8414 12.05001.8838 Entrance pupil 19.6265 123.7296 262.6743 position Exit pupil−35.5639 −48.0276 49.4999 position Front principal 23.7217 134.5036554.7428 points position Back principal 71.6422 50.9927 −0.4004 pointsposition

Numerical Examples I-3 and II-3

The zoom lens systems of Numerical Examples I-3 and II-3 correspondrespectively to Embodiments I-3 and II-3 shown in FIG. 7. Table I•II-7shows the surface data of the zoom lens systems of Numerical ExamplesI-3 and II-3. Table I•II-8 shows the aspherical data. Table I•II-9 showsvarious data.

TABLE I·II-7 (Surface data) Surface number r d nd vd Object surface ∞ ∞ 1 47.40168 1.15000 2.20000 24.0  2 32.73210 4.60560 1.49700 81.6  31811.82817 0.15000  4 29.28012 3.25450 1.77209 45.3  5 73.51295 Variable 6 23.77851 0.70000 2.20000 24.0  7 9.42084 4.40000  8 −22.78173 0.800001.72500 54.0  9 13.93477 1.72500 10* 16.62157 2.14990 1.92286 20.9 11−62.38542 0.45000 1.72500 54.0 12 60.02022 Variable 13 (Diaphragm) ∞1.20000 14 8.88082 1.65680 1.81328 37.1 15 227.60274 0.93430 16* 9.984082.13640 1.73182 52.5 17 −10.72168 0.45000 1.82217 27.4 18 5.77290Variable 19* 12.46093 2.50000 1.49190 69.9 20 −13.24787 0.45000 1.8470023.8 21 −20.44955 Variable 22 ∞ 0.78000 1.51680 64.2 23 ∞ (BF) Imagesurface ∞

TABLE I·II-8 (Aspherical data) Surface No. 10 K = 0.00000E+00, A4 =−1.14154E−05, A6 = −3.77234E−07, A8 = 4.74170E−09 A10 = −4.43720E−11Surface No. 16 K = 0.00000E+00, A4 = −1.91350E−04, A6 = −2.30283E−06, A8= −1.23140E−07 A10 = 2.39200E−09 Surface No. 19 K = 0.00000E+00, A4 =−6.46229E−05, A6 = 1.80827E−06, A8 = −2.76706E−08 A10 = 0.00000E+00

TABLE I·II-9 (Various data) Zooming ratio 17.36185 Wide-angle MiddleTelephoto limit position limit Focal length 4.7532 33.0062 82.5250F-number 2.91537 3.36011 4.67079 View angle 38.5791 6.3085 2.4788 Imageheight 3.6000 3.6000 3.6000 Overall length 73.9109 76.2516 89.0354 oflens system BF 0.88092 0.87773 0.90550 d5 0.6000 25.8935 31.8378 d1230.3595 3.6537 2.1000 d18 6.9274 4.6762 21.2415 d21 5.6506 11.65803.4581 Entrance pupil 19.1833 128.4786 242.8861 position Exit pupil−31.8559 −28.5804 72.2290 position Front principal 23.2464 124.5032420.8967 points position Back principal 69.1577 43.2454 6.5104 pointsposition

Numerical Examples I-4 and II-4

The zoom lens systems of Numerical Examples I-4 and II-4 correspondrespectively to Embodiments I-4 and II-4 shown in FIG. 10. Table I•II-10shows the surface data of the zoom lens systems of Numerical ExamplesI-4 and II-4. Table I•II-11 shows the aspherical data. Table I•II-12shows various data.

TABLE I·II-10 (Surface data) Surface number r d nd vd Object surface ∞ ∞ 1 43.82438 1.15000 2.20000 24.0  2 31.02039 5.27900 1.49700 81.6  3658.44950 0.15000  4 28.52422 3.61590 1.75034 48.7  5 68.48960 Variable 6 29.56473 0.70000 2.00000 40.0  7 8.61895 3.90870  8 −51.68615 0.800002.00000 40.0  9 11.64585 1.11860 10* 14.40520 1.99730 1.99537 20.7 11499.61576 0.30000 12 ∞ Variable 13 (Diaphragm) ∞ 1.20000 14 8.599781.74890 1.74441 49.9 15 227.60274 0.79490 16* 10.68361 2.20130 1.7672046.0 17 −8.54791 0.52740 1.80467 31.9 18 5.91886 Variable 19* 13.470202.50000 1.49264 69.8 20 −13.34321 0.45000 1.83850 24.0 21 −19.19175Variable 22 ∞ 0.78000 1.51680 64.2 23 ∞ (BF) Image surface ∞

TABLE I·II-11 (Aspherical data) Surface No. 10 K = 0.00000E+00, A4 =1.26403E−05, A6 = −3.24464E−07, A8 = 5.16296E−09 A10 = −7.88014E−11Surface No. 16 K = 0.00000E+00, A4 = −2.12912E−04, A6 = −1.22648E−06, A8= −2.48503E−07 A10 = 6.20350E−09 Surface No. 19 K = 0.00000E+00, A4 =−8.34287E−05, A6 = 2.95627E−06, A8 = −6.11855E−08 A10 = 0.00000E+00

TABLE I·II-12 (Various data) Zooming ratio 19.25092 Wide-angle MiddleTelephoto limit position limit Focal length 4.6667 30.0051 89.8390F-number 2.91703 3.53914 4.75267 View angle 39.0420 6.9132 2.2857 Imageheight 3.6000 3.6000 3.6000 Overall length 71.0108 73.8911 88.8837 oflens system BF 0.88090 0.87889 0.90694 d5 0.6000 24.2513 32.4604 d1228.5134 4.2216 2.1880 d18 5.0635 2.2496 20.6447 d21 6.7310 13.06773.4617 Entrance pupil 19.4202 112.7683 269.9674 position Exit pupil−25.5549 −23.9178 75.6116 position Front principal 23.2631 106.4658467.8458 points position Back principal 66.3441 43.8859 −0.9553 pointsposition

Numerical Examples I-5 and II-5

The zoom lens systems of Numerical Examples I-5 and II-5 correspondrespectively to Embodiments I-5 and II-5 shown in FIG. 13. Table I•II-13shows the surface data of the zoom lens systems of Numerical ExamplesI-5 and II-5. Table I•II-14 shows the aspherical data. Table I•II-15shows various data.

TABLE I.II-13 (Surface data) Surface number r d nd vd Object surface ∞ ∞ 1 54.95769 1.15000 1.84666 23.8  2 33.68335 5.33100 1.49700 81.6  3−358.26960 0.15000  4 29.22272 3.40000 1.72916 54.7  5 71.95118 Variable 6* 200.99950 1.40000 1.80470 41.0  7* 7.36029 4.00000  8 −33.583370.80000 1.77250 49.6  9 13.29976 0.69390 10 13.65144 2.10000 1.9228620.9 11 162.11920 Variable 12 (Diaphragm) ∞ 1.20000 13 6.66982 2.000001.49700 81.6 14 75.59153 2.60000 15* 13.37576 1.70000 1.74993 45.4 16−11.69083 0.45000 1.80610 33.3 17 9.13583 Variable 18* 16.30295 2.900001.60602 57.4 19 −12.50230 0.55000 1.68893 31.2 20 −38.77835 Variable 21∞ 0.90000 1.51633 64.0 22 ∞ (BF) Image surface ∞

TABLE I.II-14 (Aspherical data) Surface No. 6 K = 0.00000E+00, A4 =7.79768E−05, A6 = −2.12141E−07, A8 = −7.61782E−09 A10 = 4.77942E−11Surface No. 7 K = 0.00000E+00, A4 = 6.66509E−05, A6 = −2.93266E−06, A8 =2.74874E−07 A10 = −5.69183E−09 Surface No. 15 K = 0.00000E+00, A4 =−4.94612E−04, A6 = −7.34009E−06, A8 = −9.58053E−07 A10 = 2.36960E−08Surface No. 18 K = 0.00000E+00, A4 = −1.70925E−05, A6 = 1.22307E−06, A8= −1.87306E−08 A10 = 0.00000E+00

TABLE I.II-15 (Various data) Zooming ratio 19.30843 Wide-angle MiddleTelephoto limit position limit Focal length 4.7492 30.0052 91.6997F-number 2.90658 3.72119 4.58238 View angle 38.8247 6.8503 2.2304 Imageheight 3.6000 3.6000 3.6000 Overall length 72.9618 79.7551 90.0796 oflens system BF 0.92610 0.90181 0.89690 d5 0.6000 21.4792 30.0457 d1128.1807 4.9031 2.1000 d17 4.5971 6.3517 21.1363 d20 7.3330 14.79444.5758 Entrance pupil 18.8931 97.6963 253.4224 position Exit pupil−28.2798 −43.1524 97.4921 position Front principal 22.8701 107.2651432.1745 points position Back principal 68.2126 49.7499 −1.6201 pointsposition

The following Table 1-16 and Table II-16 show the corresponding valuesto the individual conditions in the zoom lens system of the numericalexamples.

Table I-16 (Corresponding Values to Conditions)

TABLE 1 Numerical Example Condition I-1 I-2 I-3 I-4 I-5  (8) dG3/dG0.213 0.199 0.188 0.194 0.231  (1) (f₄ · f_(W) · tanω)/L_(W) 0.114 0.1140.114 0.119 0.123  (2) f₃/f₄ 0.965 0.941 0.937 0.942 0.876  (3) (nd₄− 1) + (nd₆ − 1) 2.200 1.827 2.123 1.995 1.728  (4) nd₁ − nd₂ 0.7030.350 0.703 0.703 0.350  (5) (nd₁ − 1) + (nd₃ − 1) 1.952 1.450 1.9721.950 1.576  (9) f₃ ² + f₄ ²)/|f₂| 2.81 3.15 2.85 2.97 3.45 (10)m_(2T)/m_(34T) 3.470 2.598 2.772 3.275 3.181 (I · II-11) d1NG/d1G 0.11580.1221 0.1255 0.1128 0.1146 (12) f_(W) · tan(ω − ω₀) 0.11625 0.156810.11943 0.11361 0.13778 (13) f₄/f_(T) 0.226 0.189 0.229 0.210 0.230 (14)|M₁/M₂| 0.730 1.005 0.659 0.860 1.215 (15) |M₃/M₂| 0.484 0.765 0.5290.594 0.976 (16) (m_(2T)/m_(2W))/(f_(T)/f_(W)) 0.550 0.431 0.480 0.5110.521 (17) m_(3T)/m_(3W) 1.504 1.572 1.726 1.457 1.519 (18) (f₃ ² + f₄²)/(f_(W) · tanω) 6.83 7.07 6.82 6.83 7.34 (19) (L_(T) − L_(W))/(f_(W) ·tanω) 3.99 5.12 3.99 4.72 4.48 (20) (L_(T) · f_(T))/f₄(f_(W) · tanω)104.2 133.1 102.7 112.1 102.4 (21) (L_(W) · f_(T))/f₄(f_(W) · tanω) 86.5106.0 85.2 89.5 82.9 (22) f₃/f_(W) · tanω 4.75 4.85 4.67 4.68 4.84

Table II-16 (Corresponding Values to Conditions)

TABLE 2 Numerical Example Condition II-1 II-2 II-3 II-4 II-5  (9) f₃ ² +f₄ ²)/|f₂| 2.81 3.15 2.85 2.97 3.45  (1) (f₄ · f_(W) · tanω)/L_(W) 0.1140.114 0.114 0.119 0.123  (2) f₃/f₄ 0.965 0.941 0.937 0.942 0.876  (3)(nd₄ − 1) + (nd₆ − 1) 2.200 1.827 2.123 1.995 1.728  (4) nd₁ − nd₂ 0.7030.350 0.703 0.703 0.350  (5) (nd₁ − 1) + (nd₃ − 1) 1.952 1.450 1.9721.950 1.576  (8) dG3/dG 0.213 0.199 0.188 0.194 0.231 (10)m_(2T)/m_(34T) 3.470 2.598 2.772 3.275 3.181 (I · II-11) d1NG/d1G 0.11580.1221 0.1255 0.1128 0.1146 (12) f_(W) · tan(ω − ω₀) 0.11625 0.156810.11943 0.11361 0.13778 (13) f₄/f_(T) 0.226 0.189 0.229 0.210 0.230 (14)|M₁/M₂| 0.730 1.005 0.659 0.860 1.215 (15) |M₃/M₂| 0.484 0.765 0.5290.594 0.976 (16) (m_(2T)/m_(2W))/(f_(T)/f_(W)) 0.550 0.431 0.480 0.5110.521 (17) m_(3T)/m_(3W) 1.504 1.572 1.726 1.457 1.519 (18) (f₃ ² + f₄²)/(f_(W) · tanω) 6.83 7.07 6.82 6.83 7.34 (19) (L_(T) − L_(W))/(f_(W) ·tanω) 3.99 5.12 3.99 4.72 4.48 (20) (L_(T) · f_(T))/f₄(f_(W) · tanω)104.2 133.1 102.7 112.1 102.4 (21) (L_(W) · f_(T))/f₄(f_(W) · tanω) 86.5106.0 85.2 89.5 82.9 (22) f₃/f_(W) · tanω 4.75 4.85 4.67 4.68 4.84

Numerical Example III-1

The zoom lens system of Numerical Example III-1 corresponds toEmbodiment III-1 shown in FIG. 17. Table III-1 shows the surface data ofthe zoom lens system of Numerical Example III-1. Table III-2 shows theaspherical data. Table III-3 shows various data.

TABLE III-1 (Surface data) Surface number r d nd vd Object surface ∞ ∞ 1 48.06627 1.31770 1.84666 23.8  2 31.48376 4.91580 1.49700 81.6  31728.23379 0.15000  4 27.88601 3.35970 1.73057 52.7  5 60.86419 Variable 6 39.64833 0.70000 2.00060 25.5  7* 7.55348 4.40000  8 −22.276150.98830 1.72949 53.0  9 16.58189 0.67210 10 16.63263 1.94860 1.9459518.0 11 −137.62919 Variable 12 (Diaphragm) ∞ 1.20000 13 8.51724 1.794501.68197 56.2 14 134.42539 2.46100 15* 10.64755 2.00610 1.67606 53.7 16−8.26781 0.45330 1.72936 32.4 17 6.74795 Variable 18* 12.89946 2.500001.53888 65.5 19 −15.41242 0.45000 1.84541 24.2 20 −29.55429 Variable 21∞ 0.78000 1.51680 64.2 22 ∞ (BF) Image surface ∞

TABLE III-2 (Aspherical data) Surface No. 7 K = 0.00000E+00, A4 =−2.33390E−05, A6 = −1.61626E−06, A8 = 4.05408E−08 A10 = −7.54173E−10Surface No. 15 K = 0.00000E+00, A4 = −3.37336E−04, A6 = −2.41260E−06, A8= −4.80071E−07 A10 = 1.21221E−08 Surface No. 18 K = 0.00000E+00, A4 =−2.10927E−05, A6 = 1.48017E−06, A8 = −1.82833E−08 A10 = 0.00000E+00

TABLE III-3 (Various data) Zooming ratio 17.67284 Wide-angle MiddleTelephoto limit position limit Focal length 4.7526 33.0002 83.9918F-number 2.92199 3.34254 5.12386 View angle 38.5613 6.2952 2.4247 Imageheight 3.6000 3.6000 3.6000 Overall length 73.9064 75.5308 88.5709 oflens system BF 0.87657 0.86700 0.84665 d5 0.6000 24.7699 29.6745 d1130.6217 4.0296 2.4000 d17 6.6771 4.5673 23.3280 d20 5.0339 11.19992.2246 Entrance pupil 18.6139 125.2091 213.4676 position Exit pupil−33.3561 −30.4634 66.7590 position Front principal 22.7067 123.4503404.4897 points position Back principal 69.1538 42.5306 4.5791 pointsposition Magnification of zoom lens unit Lens Initial Wide-angle MiddleTelephoto unit surface No. limit position limit 1 1 0.00000 0.000000.00000 2 6 −0.26263 −0.92704 −1.90494 3 12 −0.62020 −2.46243 −1.22591 418 0.60691 0.30070 0.74813

Numerical Example III-2

The zoom lens system of Numerical Example III-2 corresponds toEmbodiment III-2 shown in FIG. 20. Table III-4 shows the surface data ofthe zoom lens system of Numerical Example III-2. Table III-5 shows theaspherical data. Table III-6 shows various data.

TABLE III-4 (Surface data) Surface number r d nd vd Object surface ∞ ∞ 1 45.58027 0.29880 1.84666 23.8  2 29.13959 4.64030 1.49700 81.6  33144.16519 0.15000  4 26.07049 3.15470 1.72500 54.0  5 64.13617 Variable 6* 113.44694 1.40000 1.80470 41.0  7* 6.91788 5.01430  8 −14.585620.30000 1.71891 54.3  9 50.43219 0.30640 10 20.56042 1.77880 1.8470023.8 11 −25.90405 0.55000 1.72500 54.0 12 −284.10307 Variable 13(Diaphragm) ∞ 1.20000 14* 10.21465 2.87650 1.59050 61.9 15 −29.792412.19600 16 10.32052 1.11950 1.66979 56.9 17 −41.94030 0.44920 1.7116631.8 18 6.68552 Variable 19* 14.65464 2.88740 1.60602 57.4 20 −16.441330.54980 1.84704 23.8 21 −37.86003 Variable 22 ∞ 0.78000 1.51680 64.2 23∞ (BF) Image surface ∞

TABLE III-5 (Aspherical data) Surface No. 6 K = 0.00000E+00, A4 =2.01937E−04, A6 = −2.56319E−06, A8 = 1.52224E−08 A10 = −3.89292E−11Surface No. 7 K = 0.00000E+00, A4 = 2.05664E−04, A6 = 2.06908E−06, A8 =4.49468E−08 A10 = −1.25683E−09 Surface No. 14 K = 0.00000E+00, A4 =−1.72554E−04, A6 = 1.33674E−06, A8 = −2.02892E−07 A10 = 7.52576E−09Surface No. 19 K = 0.00000E+00, A4 = −1.62255E−05, A6 = 6.87596E−07, A8= −4.80109E−09 A10 = 0.00000E+00

TABLE III-6 (Various data) Zooming ratio 17.66807 Wide-angle MiddleTelephoto limit position limit Focal length 4.7532 32.9970 83.9796F-number 2.92135 3.38151 5.08174 View angle 38.6042 6.2756 2.4298 Imageheight 3.6000 3.6000 3.6000 Overall length 70.6847 72.7597 88.0179 oflens system BF 1.17730 0.87395 0.89751 d5 0.6000 21.7525 26.3849 d1226.7016 3.2299 2.1000 d18 6.5447 4.4121 25.5257 d21 6.0094 12.83953.4581 Entrance pupil 17.8051 111.6713 199.0761 position Exit pupil−34.9864 −32.7508 58.0796 position Front principal 21.9335 112.2873406.3912 points position Back principal 65.9315 39.7627 4.0383 pointsposition Magnification of zoom lens unit Lens Initial Wide-angle MiddleTelephoto unit surface No. limit position limit 1 1 0.00000 0.000000.00000 2 6 −0.26635 −0.92800 −2.03523 3 13 −0.76090 −3.59377 −1.40660 419 0.54536 0.23007 0.68213

Numerical Example III-3

The zoom lens system of Numerical Example III-3 corresponds toEmbodiment III-3 shown in FIG. 23. Table III-7 shows the surface data ofthe zoom lens system of Numerical Example III-3. Table III-8 shows theaspherical data. Table III-9 shows various data.

TABLE III-7 (Surface data) Surface number r d nd vd Object surface ∞ ∞ 1 45.32568 1.30000 1.84666 23.8  2 31.96732 6.00000 1.49700 81.6  3−465.95760 0.15000  4 31.02235 3.20000 1.60311 60.7  5 70.61610 Variable 6 101.53090 0.70000 1.90366 31.3  7 7.86890 4.70000  8* −20.554970.80000 1.66547 55.2  9* 31.47034 0.85000 10 20.42499 2.45000 1.9228620.9 11 −33.42648 0.60000 1.83481 42.7 12 140.41630 Variable 13(Diaphragm) ∞ 2.30000 14 8.34831 1.90000 1.69680 55.5 15 53.232192.25000 16* 10.01290 1.58000 1.66547 55.2 17 −22.10466 0.50000 1.7173629.5 18 6.46268 Variable 19* 13.27992 3.80000 1.60602 57.4 20 −10.796850.60000 1.68893 31.2 21 −52.08229 Variable 22 ∞ 1.50000 1.51633 64.0 23∞ (BF) Image surface ∞

TABLE III-8 (Aspherical data) Surface No. 8 K = −6.51516E+00, A4 =1.83172E−04, A6 = −2.80928E−06, A8 = 3.42057E−08 A10 = 9.87349E−10, A12= −3.74201E−11 Surface No. 9 K = 1.96222E+01, A4 = 1.46869E−04, A6 =−5.98441E−06, A8 = 1.36308E−07 A10 = −3.03194E−09, A12 = −4.21254E−12Surface No. 16 K = 0.00000E+00, A4 = −3.48709E−04, A6 = −1.57547E−06, A8= −9.11687E−07 A10 = 4.51561E−08, A12 = 0.00000E+00 Surface No. 19 K =0.00000E+00, A4 = −7.49537E−06, A6 = 1.22932E−06, A8 = −1.00174E−08 A10= 0.00000E+00, A12 = 0.00000E+00

TABLE III-9 (Various data) Zooming ratio 22.24156 Wide-angle MiddleTelephoto limit position limit Focal length 4.7300 32.3327 105.2017F-number 2.93911 3.38403 5.23447 View angle 39.1735 6.3700 1.9176 Imageheight 3.6000 3.6000 3.6000 Overall length 77.0121 82.2972 96.7586 oflens system BF 0.37000 0.36999 0.36998 d5 0.6545 25.5975 32.6534 d1228.6039 3.0484 1.3091 d18 6.5672 6.0613 26.5797 d21 5.6364 12.04010.6665 Entrance pupil 19.6238 126.0506 272.8794 position Exit pupil−38.6210 −42.0732 48.4452 position Front principal 23.7800 133.7527608.2910 points position Back principal 72.2821 49.9646 −8.4431 pointsposition Magnification of zoom lens unit Lens Initial Wide-angle MiddleTelephoto unit surface No. limit position limit 1 1 0.00000 0.000000.00000 2 6 −0.24250 −0.80342 −2.32434 3 13 −0.73360 −3.92128 −1.15289 419 0.52565 0.20290 0.77615

Numerical Example III-4

The zoom lens system of Numerical Example III-4 corresponds toEmbodiment III-4 shown in FIG. 26. Table III-10 shows the surface dataof the zoom lens system of Numerical Example III-4. Table III-11 showsthe aspherical data. Table III-12 shows various data.

TABLE III-10 (Surface data) Surface number r d nd vd Object surface ∞ ∞ 1 46.44500 1.30000 1.84666 23.8  2 32.72500 6.00000 1.49700 81.6  3−982.64300 0.15000  4 31.73700 3.20000 1.60311 60.7  5 80.08200 Variable 6 67.96500 0.70000 1.90366 31.3  7 7.58200 4.70000  8* −19.909000.80000 1.66547 55.2  9* 30.64300 0.85000 10 20.43900 2.45000 1.9228620.9 11 −35.61000 0.60000 1.83481 42.7 12 205.15200 Variable 13(Diaphragm) ∞ 2.30000 14 8.34800 1.90000 1.69680 55.5 15 53.887002.25000 16* 9.73700 1.58000 1.66547 55.2 17 −19.97400 0.50000 1.7173629.5 18 6.45700 Variable 19* 13.57200 3.80000 1.60602 57.4 20 −11.077000.60000 1.68893 31.2 21 −48.33800 Variable 22 ∞ 1.50000 1.51633 64.0 23∞ (BF) Image surface ∞

TABLE III-11 (Aspherical data) Surface No. 8 K = −6.51516E+00, A4 =1.89183E−04, A6 = −2.49064E−06, A8 = 2.77094E−08 A10 = 6.84399E−10, A12= −5.15964E−11 Surface No. 9 K = 1.96222E+01, A4 = 1.45171E−04, A6 =−5.85108E−06, A8 = 1.29651E−07 A10 = −3.48894E−09, A12 = −1.54662E−11Surface No. 16 K = 0.00000E+00, A4 = −3.55330E−04, A6 = −1.23807E−06, A8= −8.99076E−07 A10 = 4.13198E−08, A12 = 0.00000E+00 Surface No. 19 K =0.00000E+00, A4 = −1.52310E−05, A6 = 8.65343E−07, A8 = −6.40898E−09 A10= 0.00000E+00, A12 = 0.00000E+00

TABLE III-12 (Various data) Zooming ratio 16.56444 Wide-angle MiddleTelephoto limit position limit Focal length 4.5227 32.1468 74.9158F-number 2.67412 3.40666 4.20747 View angle 40.1340 6.4020 2.7184 Imageheight 3.6000 3.6000 3.6000 Overall length 75.6478 82.5569 94.6221 oflens system BF 4.61064 2.39245 4.30248 d5 0.6545 25.5587 32.3597 d1228.4185 2.2206 1.3091 d18 5.4751 7.2857 20.7204 d21 1.3091 9.9194 0.7504Entrance pupil 19.4978 118.9789 242.2873 position Exit pupil −28.7952−48.5941 77.6649 position Front principal 23.4081 130.8573 393.7053points position Back principal 71.1252 50.4101 19.7062 points positionMagnification of zoom lens unit Lens Initial Wide-angle Middle Telephotounit surface No. limit position limit 1 1 0.00000 0.00000 0.00000 2 6−0.24005 −0.75819 −1.84676 3 13 −0.69140 −3.95981 −1.37544 4 19 0.531870.20899 0.57566

The following Table III-13 shows the corresponding values to theindividual conditions in the zoom lens systems of the numericalexamples.

Table III-13 (Corresponding Values to Conditions)

TABLE 3 Numerical Example Condition III-1 III-2 III-3 III-4 (III-11)d1NG/d1G 0.13524 0.03625 0.12207 0.12207  (1) (f₄ · f_(W) · tanω)/L_(W)0.118 0.125 0.114 0.110  (2) f₃/f₄ 0.854 0.851 0.941 0.917  (3) (nd₄− 1) + (nd₆ − 1) 1.947 1.652 1.827 1.827  (8) dG3/dG 0.236 0.240 0.1990.199  (9) f₃ ² + f₄ ²)/|f₂| 2.98 3.44 3.15 3.07 (10) m_(2T)/m_(34T)2.080 2.121 2.598 2.332 (12) f_(W) · tan(ω − ω₀) 0.1176 0.1215 0.15680.1275 (13) f₄/f_(T) 0.239 0.246 0.189 0.264 (14) |M₁/M₂| 1.018 0.9091.005 1.490 (15) |M₃/M₂| 0.959 0.847 0.765 1.129 (16)(m_(2T)/m_(2W))/(f_(T)/f_(W)) 0.411 0.432 0.431 0.464 (17) m_(3T)/m_(3W)1.974 1.849 1.572 1.990 (18) (f₃ ² + f₄ ²)/(f_(W) · tanω) 6.98 7.16 7.077.04 (19) (L_(T) − L_(W))/(f_(W) · tanω) 3.87 4.57 5.12 4.98 (20) (L_(T)· f_(T))/f₄(f_(W) · tanω) 97.7 94.1 133.1 97.2 (21) (L_(W) ·f_(T))/f₄(f_(W) · tanω) 81.5 75.6 106.0 78.3 (22) f₃/f_(W) · tanω 4.534.64 4.85 4.76

INDUSTRIAL APPLICABILITY

The zoom lens system according to the present invention is applicable toa digital input device such as a digital still camera, a digital videocamera, a mobile telephone, a PDA (Personal Digital Assistance), asurveillance camera in a surveillance system, a Web camera or avehicle-mounted camera. In particular, the zoom lens system according tothe present invention is suitable for a photographing optical systemwhere high image quality is required like in a digital still camera, adigital video camera or the like.

1. A zoom lens system, in order from an object side to an image side,comprising a first lens unit having positive optical power, a secondlens unit having negative optical power, a third lens unit havingpositive optical power, and a fourth lens unit having positive opticalpower, wherein in zooming from a wide-angle limit to a telephoto limit,all of the first lens unit, the second lens unit, the third lens unitand the fourth lens unit move along an optical axis, and wherein thefollowing condition (8) is satisfied:0.15<dG3/dG<0.27  (8) (here, 16<f_(T)/f_(W) and ω>35) where, dG3 is anoptical axial center thickness of the third lens unit, dG is a sum ofthe optical axial thicknesses of the first lens unit, the second lensunit, the third lens unit and the fourth lens unit, ω is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 2. The zoom lens system as claimed inclaim 1, wherein the third lens unit moves in a direction perpendicularto the optical axis.
 3. An imaging device capable of outputting anoptical image of an object as an electric image signal, comprising: azoom lens system that forms the optical image of the object; and animage sensor that converts the optical image formed by the zoom lenssystem into the electric image signal, wherein in the zoom lens system,the zoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein in zooming from a wide-angle limit to a telephoto limit, all ofthe first lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein the followingcondition (8) is satisfied:0.15<dG3/dG<0.27  (8) (here, 16<f_(T)/f_(W) and ω>35) where, dG3 is anoptical axial center thickness of the third lens unit, dG is a sum ofthe optical axial thicknesses of the first lens unit, the second lensunit, the third lens unit and the fourth lens unit, ω is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 4. A camera for converting an opticalimage of an object into an electric image signal and then performing atleast one of displaying and storing of the converted image signal,comprising an imaging device including a zoom lens system that forms theoptical image of the object and an image sensor that converts theoptical image formed by the zoom lens system into the electric imagesignal, wherein in the zoom lens system, the zoom lens system, in orderfrom an object side to an image side, comprises a first lens unit havingpositive optical power, a second lens unit having negative opticalpower, a third lens unit having positive optical power, and a fourthlens unit having positive optical power, wherein in zooming from awide-angle limit to a telephoto limit, all of the first lens unit, thesecond lens unit, the third lens unit and the fourth lens unit movealong an optical axis, and wherein the following condition (8) issatisfied:0.15<dG3/dG<0.27  (8) (here, 16<f_(T)/f_(W) and ω>35) where, dG3 is anoptical axial center thickness of the third lens unit, dG is a sum ofthe optical axial thicknesses of the first lens unit, the second lensunit, the third lens unit and the fourth lens unit, ω is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 5. A zoom lens system, in order from anobject side to an image side, comprising a first lens unit havingpositive optical power, a second lens unit having negative opticalpower, a third lens unit having positive optical power, and a fourthlens unit having positive optical power, wherein in zooming from awide-angle limit to a telephoto limit, all of the first lens unit, thesecond lens unit, the third lens unit and the fourth lens unit movealong an optical axis, and wherein the following condition (9) issatisfied:2.7<√(f ₃ ² +f ₄ ²)/|f ₂|<3.6  (9) (here, 16<f_(T)/f_(W) and ω>35)where, f₂ is a focal length of the second lens unit, f₃ is a focallength of the third lens unit, f₄ is a focal length of the fourth lensunit, ω is a half view angle (°) at a wide-angle limit, f_(T) is a focallength of the entire system at a telephoto limit, and f_(W) is a focallength of the entire system at a wide-angle limit.
 6. The zoom lenssystem as claimed in claim 5, wherein the third lens unit moves in adirection perpendicular to the optical axis.
 7. An imaging devicecapable of outputting an optical image of an object as an electric imagesignal, comprising: a zoom lens system that forms the optical image ofthe object; and an image sensor that converts the optical image formedby the zoom lens system into the electric image signal, wherein in thezoom lens system, the zoom lens system, in order from an object side toan image side, comprises a first lens unit having positive opticalpower, a second lens unit having negative optical power, a third lensunit having positive optical power, and a fourth lens unit havingpositive optical power, wherein in zooming from a wide-angle limit to atelephoto limit, all of the first lens unit, the second lens unit, thethird lens unit and the fourth lens unit move along an optical axis, andwherein the following condition (9) is satisfied:2.7<√(f ₃ ² +f ₄ ²)/|f ₂|<3.6  (9) (here, 16<f_(T)/f_(W) and ω>35)where, f₂ is a focal length of the second lens unit, f₃ is a focallength of the third lens unit, f₄ is a focal length of the fourth lensunit, ω is a half view angle (°) at a wide-angle limit, f_(T) is a focallength of the entire system at a telephoto limit, and f_(W) is a focallength of the entire system at a wide-angle limit.
 8. A camera forconverting an optical image of an object into an electric image signaland then performing at least one of displaying and storing of theconverted image signal, comprising an imaging device including a zoomlens system that forms the optical image of the object and an imagesensor that converts the optical image formed by the zoom lens systeminto the electric image signal, wherein in the zoom lens system, thezoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein in zooming from a wide-angle limit to a telephoto limit, all ofthe first lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein the followingcondition (9) is satisfied:2.7<√(f ₃ ² +f ₄ ²)/|f ₂|<3.6  (9) (here, 16<f_(T)/f_(W) and ω>35)where, f₂ is a focal length of the second lens unit, f₃ is a focallength of the third lens unit, f₄ is a focal length of the fourth lensunit, ω is a half view angle (°) at a wide-angle limit, f_(T) is a focallength of the entire system at a telephoto limit, and f_(W) is a focallength of the entire system at a wide-angle limit.
 9. A zoom lenssystem, in order from an object side to an image side, comprising afirst lens unit having positive optical power, a second lens unit havingnegative optical power, a third lens unit having positive optical power,and a fourth lens unit having positive optical power, wherein in zoomingfrom a wide-angle limit to a telephoto limit, all of the first lensunit, the second lens unit, the third lens unit and the fourth lens unitmove along an optical axis, and wherein the following condition (III-11)is satisfied:0.036<d1NG/d1G<0.140  (III-11) (here, 16<f_(T)/f_(W) and ω>35) where,d1NG is an optical axial center thickness of the lens element havingnegative optical power contained in the first lens unit, d1G is anoptical axial center thickness of the first lens unit, ω is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 10. The zoom lens system as claimed inclaim 9, wherein the third lens unit moves in a direction perpendicularto the optical axis.
 11. An imaging device capable of outputting anoptical image of an object as an electric image signal, comprising: azoom lens system that forms the optical image of the object; and animage sensor that converts the optical image formed by the zoom lenssystem into the electric image signal, wherein in the zoom lens system,the zoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein in zooming from a wide-angle limit to a telephoto limit, all ofthe first lens unit, the second lens unit, the third lens unit and thefourth lens unit move along an optical axis, and wherein the followingcondition (III-11) is satisfied:0.036<d1NG/d1G<0.140  (III-11) (here, 16<f_(T)/f_(W) and ω>35) where,d1NG is an optical axial center thickness of the lens element havingnegative optical power contained in the first lens unit, d1G is anoptical axial center thickness of the first lens unit, ω is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 12. A camera for converting an opticalimage of an object into an electric image signal and then performing atleast one of displaying and storing of the converted image signal,comprising an imaging device including a zoom lens system that forms theoptical image of the object and an image sensor that converts theoptical image formed by the zoom lens system into the electric imagesignal, wherein in the zoom lens system, the zoom lens system, in orderfrom an object side to an image side, comprises a first lens unit havingpositive optical power, a second lens unit having negative opticalpower, a third lens unit having positive optical power, and a fourthlens unit having positive optical power, wherein in zooming from awide-angle limit to a telephoto limit, all of the first lens unit, thesecond lens unit, the third lens unit and the fourth lens unit movealong an optical axis, and wherein the following condition (III-11) issatisfied:0.036<d1NG/d1G<0.140  (III-11) (here, 16<f_(T)/f_(W) and ω>35) where,d1NG is an optical axial center thickness of the lens element havingnegative optical power contained in the first lens unit, d1G is anoptical axial center thickness of the first lens unit, ω is a half viewangle (°) at a wide-angle limit, f_(T) is a focal length of the entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.